Uplink reference signal transmitting or receiving method in wireless communication system, and apparatus therefor

ABSTRACT

Provided is an uplink reference signal transmitting method for a terminal configured to support a length of a transmission time interval (TTI) in a wireless communication system according to an embodiment of the present invention. The method is performed by a terminal and may comprise the steps of: receiving configuration information associated with an uplink reference signal for a plurality of TTIs from a base station; and transmitting an uplink reference signal in at least one TTI from among the plurality of TTIs, using the received configuration information, wherein the configuration information may be included in signaling that schedules at least one TTI from among the plurality of TTIs.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of transmitting or receiving an uplinkreference signal in a wireless communication system and an apparatustherefor.

BACKGROUND ART

In a wireless cellular communication system, discussion on atransmission/reception method capable of reducing latency as much aspossible is in progress. In particular, according to the method, data istransmitted as soon as possible within a short time period using a shortTTI (transmission time interval) for a service/UE sensitive to latencyand a response is transmitted within a short time period in response tothe data. On the contrary, it is able to transmit/receive data using alonger TTI for a service/UE less sensitive to latency. For a service/UEsensitive to power efficiency rather than latency, it may be able torepeatedly transmit data using the same low power or transmit data bymore extending TTI. The present invention proposes a method ofallocating a resource of a reference signal, a transmission method, anda multiplexing scheme to enable the abovementioned operations.

DISCLOSURE OF THE INVENTION Technical Task

A technical task of the present invention is to provide a method oftransmitting or receiving an uplink reference signal in a wirelesscommunication system and an operation related to the method.

Technical tasks obtainable from the present invention are non-limitedthe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting an uplink reference signalfor a terminal configured to support multiple TTI (transmission timeinterval) lengths in a wireless communication system, includes receivingconfiguration information on an uplink reference signal for a pluralityof TTIs from a base station, and transmitting an uplink reference signalin at least one TTI from among the plurality of TTIs using the receivedconfiguration information. In this case, the configuration informationmay be included in signaling that schedules the at least one TTI fromamong the plurality of TTIs.

Additionally or alternatively, the uplink reference signal may betransmitted in a symbol of each of the at least one TTI.

Additionally or alternatively, the configuration information may beincluded in downlink control information that schedules a TTI from amongthe plurality of TTIs.

Additionally or alternatively, the configuration information may includea bit field indicating TTIs in which the uplink reference signal is tobe transmitted, and the bit field may indicate whether or not the uplinkreference signal is transmitted in a respective one of a predeterminednumber of contiguous TTIs including a TTI scheduled by the configurationinformation.

Additionally or alternatively, the configuration information indicatesone of a plurality of candidate patterns in which the uplink referencesignal is to be transmitted, and each of the plurality of candidatepatterns may indicate a TTI or a symbol of a TTI, included in apredetermined time duration in which the uplink reference signal istransmitted.

Additionally or alternatively, the method may further include receivinginformation on a symbol of the at least one TTI in which the uplinkreference signal is to be transmitted.

Additionally or alternatively, the configuration information includes abit field indicating a symbol of a TTI in which the uplink referencesignal is to be transmitted, and the bit field may indicate symbols of apredetermined number of contiguous TTIs including a TTI scheduled by theconfiguration information.

Additionally or alternatively, configuration information to be used fortransmitting the uplink reference signal may be included in signalingthat schedules a predetermined TTI from among the plurality of TTIs.

Additionally or alternatively, the configuration information can beincluded in signaling that schedules a TTI to which a largest uplinktransmission resource is allocated, from among the plurality of TTIs.

Additionally or alternatively, the terminal may expect that signalingfor scheduling the plurality of TTIs indicates configuration informationon the same uplink reference signal.

Additionally or alternatively, the configuration information can includeat least one selected from the group consisting of a cyclic shift, anOCC (orthogonal cover code), transmit power, RE (resource element)mapping of an uplink reference signal, and resource allocation.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, aterminal configured to support multiple TTI (transmission time interval)lengths in a wireless communication system includes a transmitter and areceiver, and a processor that controls the transmitter and thereceiver, the processor controls the receiver to receive configurationinformation on an uplink reference signal for a plurality of TTIs from abase station, controls the transmitter to transmit an uplink referencesignal in at least one TTI from among the plurality of TTIs using thereceived configuration information. In this case, the configurationinformation may be included in signaling that schedules the at least oneTTIs from among the plurality of TTIs.

Technical solutions obtainable from the present invention arenon-limited the above-mentioned technical solutions. And, otherunmentioned technical solutions can be clearly understood from thefollowing description by those having ordinary skill in the technicalfield to which the present invention pertains.

Advantageous Effects

According to one embodiment of the present invention, it is able toefficiently transmit or receive an uplink reference signal in a wirelesscommunication system.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram for an example of a radio frame structure used in awireless communication system;

FIG. 2 is a diagram for an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system;

FIG. 3 is a diagram for an example of a downlink (DL) subframe structureused in 3GPP LTE/LTE-A system;

FIG. 4 is a diagram for an example of an uplink (UL) subframe structureused in 3GPP LTE/LTE-A system;

FIG. 5 is a diagram illustrating DL reception timing and UL transmissiontiming of UEs operating with a different TTI (transmission timeinterval);

FIG. 6 illustrates a DM-RS (demodulation-reference signal) symbol sharedbetween TTIs;

FIG. 7 illustrates a DM-RS (demodulation-reference signal) symbol sharedbetween TTIs;

FIG. 8 illustrates a DM-RS (demodulation-reference signal) symbol and areserved SRS (sounding reference signal) symbol shared between TTIs;

FIG. 9 illustrates a DM-RS (demodulation-reference signal) symbol sharedbetween TTIs;

FIG. 10 illustrates an example of a DM-RS symbol shared between TTIs;

FIG. 11 illustrates an example of a DM-RS symbol shared between TTIs;

FIG. 12 illustrates an example of a DM-RS symbol shared between TTIs towhich an uplink resource of a different size is allocated and a DM-RSfor each TTI;

FIG. 13 illustrates an RE pattern to which a DM-RS is mapped accordingto a size or a length of a TTI;

FIG. 14 illustrates an RE pattern to which a DM-RS is mapped in twoconsecutive TTIs;

FIG. 15 illustrates an RE pattern to which a DM-RS is mapped inconsecutive TTIs;

FIG. 16 illustrates an additional DM-RS symbol except a DM-RS symbolshared between TTIs;

FIG. 17 illustrates a DM-RS for each TTI in a DM-RS symbol sharedbetween TTIs;

FIG. 18 is a flowchart illustrating an operation of a UE;

FIG. 19 is a block diagram of a device for implementing embodiment(s) ofthe present invention.

BEST MODE Mode for Invention

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The accompanying drawings illustrate exemplary embodiments ofthe present invention and provide a more detailed description of thepresent invention. However, the scope of the present invention shouldnot be limited thereto.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

In the present invention, a user equipment (UE) is fixed or mobile. TheUE is a device that transmits and receives user data and/or controlinformation by communicating with a base station (BS). The term ‘UE’ maybe replaced with ‘terminal equipment’, ‘Mobile Station (MS)’, ‘MobileTerminal (MT)’, ‘User Terminal (UT)’, ‘Subscriber Station (SS)’,‘wireless device’, ‘Personal Digital Assistant (PDA)’, ‘wireless modem’,‘handheld device’, etc. A BS is typically a fixed station thatcommunicates with a UE and/or another BS. The BS exchanges data andcontrol information with a UE and another BS. The term BS' may bereplaced with ‘Advanced Base Station (ABS)’, ‘Node B’, ‘evolved-Node B(eNB)’, ‘Base Transceiver System (BTS)’, ‘Access Point (AP)’,‘Processing Server (PS)’, etc. In the following description, BS iscommonly called eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal to/from a UE by communication withthe UE. Various eNBs can be used as nodes. For example, a node can be aBS, NB, eNB, pico-cell eNB (PeNB), home eNB (HeNB), relay, repeater,etc. Furthermore, a node may not be an eNB. For example, a node can be aradio remote head (RRH) or a radio remote unit (RRU). The RRH and RRUhave power levels lower than that of the eNB. Since the RRH or RRU(referred to as RRH/RRU hereinafter) is connected to an eNB through adedicated line such as an optical cable in general, cooperativecommunication according to RRH/RRU and eNB can be smoothly performedcompared to cooperative communication according to eNBs connectedthrough a wireless link. At least one antenna is installed per node. Anantenna may refer to an antenna port, a virtual antenna or an antennagroup. A node may also be called a point. Unlike a conventionalcentralized antenna system (CAS) (i.e. single node system) in whichantennas are concentrated in an eNB and controlled an eNB controller,plural nodes are spaced apart at a predetermined distance or longer in amulti-node system. The plural nodes can be managed by one or more eNBsor eNB controllers that control operations of the nodes or schedule datato be transmitted/received through the nodes. Each node may be connectedto an eNB or eNB controller managing the corresponding node via a cableor a dedicated line. In the multi-node system, the same cell identity(ID) or different cell IDs may be used for signal transmission/receptionthrough plural nodes. When plural nodes have the same cell ID, each ofthe plural nodes operates as an antenna group of a cell. If nodes havedifferent cell IDs in the multi-node system, the multi-node system canbe regarded as a multi-cell (e.g., macro-cell/femto-cell/pico-cell)system. When multiple cells respectively configured by plural nodes areoverlaid according to coverage, a network configured by multiple cellsis called a multi-tier network. The cell ID of the RRH/RRU may beidentical to or different from the cell ID of an eNB. When the RRH/RRUand eNB use different cell IDs, both the RRH/RRU and eNB operate asindependent eNBs.

In a multi-node system according to the present invention, which will bedescribed below, one or more eNBs or eNB controllers connected to pluralnodes can control the plural nodes such that signals are simultaneouslytransmitted to or received from a UE through some or all nodes. Whilethere is a difference between multi-node systems according to the natureof each node and implementation form of each node, multi-node systemsare discriminated from single node systems (e.g. CAS, conventional MIMOsystems, conventional relay systems, conventional repeater systems,etc.) since a plurality of nodes provides communication services to a UEin a predetermined time-frequency resource. Accordingly, embodiments ofthe present invention with respect to a method of performing coordinateddata transmission using some or all nodes can be applied to varioustypes of multi-node systems. For example, a node refers to an antennagroup spaced apart from another node by a predetermined distance ormore, in general. However, embodiments of the present invention, whichwill be described below, can even be applied to a case in which a noderefers to an arbitrary antenna group irrespective of node interval. Inthe case of an eNB including an X-pole (cross polarized) antenna, forexample, the embodiments of the preset invention are applicable on theassumption that the eNB controls a node composed of an H-pole antennaand a V-pole antenna.

A communication scheme through which signals are transmitted/receivedvia plural transmit (Tx)/receive (Rx) nodes, signals aretransmitted/received via at least one node selected from plural Tx/Rxnodes, or a node transmitting a downlink signal is discriminated from anode transmitting an uplink signal is called multi-eNB MIMO or CoMP(Coordinated Multi-Point Tx/Rx). Coordinated transmission schemes fromamong CoMP communication schemes can be categorized into JP (JointProcessing) and scheduling coordination. The former may be divided intoJT (Joint Transmission)/JR (Joint Reception) and DPS (Dynamic PointSelection) and the latter may be divided into CS (CoordinatedScheduling) and CB (Coordinated Beamforming). DPS may be called DCS(Dynamic Cell Selection). When JP is performed, more variouscommunication environments can be generated, compared to other CoMPschemes. JT refers to a communication scheme by which plural nodestransmit the same stream to a UE and JR refers to a communication schemeby which plural nodes receive the same stream from the UE. The UE/eNBcombine signals received from the plural nodes to restore the stream. Inthe case of JT/JR, signal transmission reliability can be improvedaccording to transmit diversity since the same stream is transmittedfrom/to plural nodes. DPS refers to a communication scheme by which asignal is transmitted/received through a node selected from plural nodesaccording to a specific rule. In the case of DPS, signal transmissionreliability can be improved because a node having a good channel statebetween the node and a UE is selected as a communication node.

In the present invention, a cell refers to a specific geographical areain which one or more nodes provide communication services. Accordingly,communication with a specific cell may mean communication with an eNB ora node providing communication services to the specific cell. Adownlink/uplink signal of a specific cell refers to a downlink/uplinksignal from/to an eNB or a node providing communication services to thespecific cell. A cell providing uplink/downlink communication servicesto a UE is called a serving cell. Furthermore, channel status/quality ofa specific cell refers to channel status/quality of a channel or acommunication link generated between an eNB or a node providingcommunication services to the specific cell and a UE. In 3GPP LTE-Asystems, a UE can measure downlink channel state from a specific nodeusing one or more CSI-RSs (Channel State Information Reference Signals)transmitted through antenna port(s) of the specific node on a CSI-RSresource allocated to the specific node. In general, neighboring nodestransmit CSI-RS resources on orthogonal CSI-RS resources. When CSI-RSresources are orthogonal, this means that the CSI-RS resources havedifferent subframe configurations and/or CSI-RS sequences which specifysubframes to which CSI-RSs are allocated according to CSI-RS resourceconfigurations, subframe offsets and transmission periods, etc. whichspecify symbols and subcarriers carrying the CSI RSs.

In the present invention, PDCCH (Physical Downlink ControlChannel)/PCFICH (Physical Control Format Indicator Channel)/PHICH(Physical Hybrid automatic repeat request Indicator Channel)/PDSCH(Physical Downlink Shared Channel) refer to a set of time-frequencyresources or resource elements respectively carrying DCI (DownlinkControl Information)/CFI (Control Format Indicator)/downlink ACK/NACK(Acknowledgement/Negative ACK)/downlink data. In addition, PUCCH(Physical Uplink Control Channel)/PUSCH (Physical Uplink SharedChannel)/PRACH (Physical Random Access Channel) refer to sets oftime-frequency resources or resource elements respectively carrying UCI(Uplink Control Information)/uplink data/random access signals. In thepresent invention, a time-frequency resource or a resource element (RE),which is allocated to or belongs toPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH, is referred to as aPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH resource. In the followingdescription, transmission of PUCCH/PUSCH/PRACH by a UE is equivalent totransmission of uplink control information/uplink data/random accesssignal through or on PUCCH/PUSCH/PRACH. Furthermore, transmission ofPDCCH/PCFICH/PHICH/PDSCH by an eNB is equivalent to transmission ofdownlink data/control information through or onPDCCH/PCFICH/PHICH/PDSCH.

FIG. 1 illustrates an exemplary radio frame structure used in a wirelesscommunication system. FIG. 1(a) illustrates a frame structure forfrequency division duplex (FDD) used in 3GPP LTE/LTE-A and FIG. 1(b)illustrates a frame structure for time division duplex (TDD) used in3GPP LTE/LTE-A.

Referring to FIG. 1, a radio frame used in 3GPP LTE/LTE-A has a lengthof 10 ms (307200 Ts) and includes 10 subframes in equal size. The 10subframes in the radio frame may be numbered. Here, Ts denotes samplingtime and is represented as Ts=1/(2048*15 kHz). Each subframe has alength of 1 ms and includes two slots. 20 slots in the radio frame canbe sequentially numbered from 0 to 19. Each slot has a length of 0.5 ms.A time for transmitting a subframe is defined as a transmission timeinterval (TTI). Time resources can be discriminated by a radio framenumber (or radio frame index), subframe number (or subframe index) and aslot number (or slot index).

The radio frame can be configured differently according to duplex mode.Downlink transmission is discriminated from uplink transmission byfrequency in FDD mode, and thus the radio frame includes only one of adownlink subframe and an uplink subframe in a specific frequency band.In TDD mode, downlink transmission is discriminated from uplinktransmission by time, and thus the radio frame includes both a downlinksubframe and an uplink subframe in a specific frequency band.

Table 1 shows DL-UL configurations of subframes in a radio frame in theTDD mode.

TABLE 1 Downlink- DL-UL to-Uplink config- Switch-point Subframe numberuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U U D DD D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5 ms DS U U U D S U U D

In Table 1, D denotes a downlink subframe, U denotes an uplink subframeand S denotes a special subframe. The special subframe includes threefields of DwPTS (Downlink Pilot TimeSlot), GP (Guard Period), and UpPTS(Uplink Pilot TimeSlot). DwPTS is a period reserved for downlinktransmission and UpPTS is a period reserved for uplink transmission.Table 2 shows special subframe configuration.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — —9 13168 · T_(s) — — —

FIG. 2 illustrates an exemplary downlink/uplink slot structure in awireless communication system. Particularly, FIG. 2 illustrates aresource grid structure in 3GPP LTE/LTE-A. A resource grid is presentper antenna port.

Referring to FIG. 2, a slot includes a plurality of OFDM (OrthogonalFrequency Division Multiplexing) symbols in the time domain and aplurality of resource blocks (RBs) in the frequency domain. An OFDMsymbol may refer to a symbol period. A signal transmitted in each slotmay be represented by a resource grid composed of N_(RB) ^(DL/UL)*N_(sc)^(RB) subcarriers and N_(symb) ^(DL/UL) OFDM symbols. Here, N_(RB) ^(DL)denotes the number of RBs in a downlink slot and N_(RB) ^(UL) denotesthe number of RBs in an uplink slot. N_(RB) ^(DL and N) _(RB) ^(UL)respectively depend on a DL transmission bandwidth and a UL transmissionbandwidth. N_(symb) ^(DL) denotes the number of OFDM symbols in thedownlink slot and N_(symb) ^(UL) denotes the number of OFDM symbols inthe uplink slot. In addition, N_(sc) ^(RB) denotes the number ofsubcarriers constructing one RB.

An OFDM symbol may be called an SC-FDM (Single Carrier FrequencyDivision Multiplexing) symbol according to multiple access scheme. Thenumber of OFDM symbols included in a slot may depend on a channelbandwidth and the length of a cyclic prefix (CP). For example, a slotincludes 7 OFDM symbols in the case of normal CP and 6 OFDM symbols inthe case of extended CP. While FIG. 2 illustrates a subframe in which aslot includes 7 OFDM symbols for convenience, embodiments of the presentinvention can be equally applied to subframes having different numbersof OFDM symbols. Referring to FIG. 2, each OFDM symbol includes N_(RB)^(DL/UL)*N_(sc) ^(RB) subcarriers in the frequency domain. Subcarriertypes can be classified into a data subcarrier for data transmission, areference signal subcarrier for reference signal transmission, and nullsubcarriers for a guard band and a direct current (DC) component. Thenull subcarrier for a DC component is a subcarrier remaining unused andis mapped to a carrier frequency (f0) during OFDM signal generation orfrequency up-conversion. The carrier frequency is also called a centerfrequency.

An RB is defined by N_(symb) ^(DL/UL) (e.g., 7) consecutive OFDM symbolsin the time domain and N_(sc) ^(RB) (e.g., 12) consecutive subcarriersin the frequency domain. For reference, a resource composed by an OFDMsymbol and a subcarrier is called a resource element (RE) or a tone.Accordingly, an RB is composed of N_(symb) ^(DL/UL)*N_(sc) ^(RB) REs.Each RE in a resource grid can be uniquely defined by an index pair (k,l) in a slot. Here, k is an index in the range of 0 to N_(symb)^(DL/UL)*N_(sc) ^(RB)−1 in the frequency domain and l is an index in therange of 0 to N_(symb) ^(DL/UL)−1.

Two RBs that occupy N_(sc) ^(RB) consecutive subcarriers in a subframeand respectively disposed in two slots of the subframe are called aphysical resource block (PRB) pair. Two RBs constituting a PRB pair havethe same PRB number (or PRB index). A virtual resource block (VRB) is alogical resource allocation unit for resource allocation. The VRB hasthe same size as that of the PRB. The VRB may be divided into alocalized VRB and a distributed VRB depending on a mapping scheme of VRBinto PRB. The localized VRBs are mapped into the PRBs, whereby VRBnumber (VRB index) corresponds to PRB number. That is, nPRB=nVRB isobtained. Numbers are given to the localized VRBs from 0 to N_(VRB)^(DL)−1, and N_(VRB) ^(DL)=N_(RB) ^(DL) is obtained. Accordingly,according to the localized mapping scheme, the VRBs having the same VRBnumber are mapped into the PRBs having the same PRB number at the firstslot and the second slot. On the other hand, the distributed VRBs aremapped into the PRBs through interleaving. Accordingly, the VRBs havingthe same VRB number may be mapped into the PRBs having different PRBnumbers at the first slot and the second slot. Two PRBs, which arerespectively located at two slots of the subframe and have the same VRBnumber, will be referred to as a pair of VRBs.

FIG. 3 illustrates a downlink (DL) subframe structure used in 3GPPLTE/LTE-A.

Referring to FIG. 3, a DL subframe is divided into a control region anda data region. A maximum of three (four) OFDM symbols located in a frontportion of a first slot within a subframe correspond to the controlregion to which a control channel is allocated. A resource regionavailable for PDCCH transmission in the DL subframe is referred to as aPDCCH region hereinafter. The remaining OFDM symbols correspond to thedata region to which a physical downlink shared chancel (PDSCH) isallocated. A resource region available for PDSCH transmission in the DLsubframe is referred to as a PDSCH region hereinafter. Examples ofdownlink control channels used in 3GPP LTE include a physical controlformat indicator channel (PCFICH), a physical downlink control channel(PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. ThePCFICH is transmitted at a first OFDM symbol of a subframe and carriesinformation regarding the number of OFDM symbols used for transmissionof control channels within the subframe. The PHICH is a response ofuplink transmission and carries an HARQ acknowledgment (ACK)/negativeacknowledgment (NACK) signal.

Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI contains resource allocation information andcontrol information for a UE or a UE group. For example, the DCIincludes a transport format and resource allocation information of adownlink shared channel (DL-SCH), a transport format and resourceallocation information of an uplink shared channel (UL-SCH), paginginformation of a paging channel (PCH), system information on the DL-SCH,information about resource allocation of an upper layer control messagesuch as a random access response transmitted on the PDSCH, a transmitcontrol command set with respect to individual UEs in a UE group, atransmit power control command, information on activation of a voiceover IP (VoIP), downlink assignment index (DAI), etc. The transportformat and resource allocation information of the DL-SCH are also calledDL scheduling information or a DL grant and the transport format andresource allocation information of the UL-SCH are also called ULscheduling information or a UL grant. The size and purpose of DCIcarried on a PDCCH depend on DCI format and the size thereof may bevaried according to coding rate. Various formats, for example, formats 0and 4 for uplink and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3Afor downlink, have been defined in 3GPP LTE. Control information such asa hopping flag, information on RB allocation, modulation coding scheme(MCS), redundancy version (RV), new data indicator (NDI), information ontransmit power control (TPC), cyclic shift demodulation reference signal(DMRS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI), etc. is selected andcombined based on DCI format and transmitted to a UE as DCI.

In general, a DCI format for a UE depends on transmission mode (TM) setfor the UE. In other words, only a DCI format corresponding to aspecific TM can be used for a UE configured in the specific TM.

A PDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups(REGs). For example, a CCE corresponds to 9 REGs and an REG correspondsto 4 REs. 3GPP LTE defines a CCE set in which a PDCCH can be located foreach UE. A CCE set from which a UE can detect a PDCCH thereof is calleda PDCCH search space, simply, search space. An individual resourcethrough which the PDCCH can be transmitted within the search space iscalled a PDCCH candidate. A set of PDCCH candidates to be monitored bythe UE is defined as the search space. In 3GPP LTE/LTE-A, search spacesfor DCI formats may have different sizes and include a dedicated searchspace and a common search space. The dedicated search space is aUE-specific search space and is configured for each UE. The commonsearch space is configured for a plurality of UEs. Aggregation levelsdefining the search space is as follows.

TABLE 3 Search Space Aggregation Size Number of PDCCH Type Level L [inCCEs] candidates M^((L)) UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 416 4 8 16 2

A PDCCH candidate corresponds to 1, 2, 4 or 8 CCEs according to CCEaggregation level. An eNB transmits a PDCCH (DCI) on an arbitrary PDCCHcandidate with in a search space and a UE monitors the search space todetect the PDCCH (DCI). Here, monitoring refers to attempting to decodeeach PDCCH in the corresponding search space according to all monitoredDCI formats. The UE can detect the PDCCH thereof by monitoring pluralPDCCHs. Since the UE does not know the position in which the PDCCHthereof is transmitted, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having the IDthereof is detected. This process is called blind detection (or blinddecoding (BD)).

The eNB can transmit data for a UE or a UE group through the dataregion. Data transmitted through the data region may be called userdata. For transmission of the user data, a physical downlink sharedchannel (PDSCH) may be allocated to the data region. A paging channel(PCH) and downlink-shared channel (DL-SCH) are transmitted through thePDSCH. The UE can read data transmitted through the PDSCH by decodingcontrol information transmitted through a PDCCH. Informationrepresenting a UE or a UE group to which data on the PDSCH istransmitted, how the UE or UE group receives and decodes the PDSCH data,etc. is included in the PDCCH and transmitted. For example, if aspecific PDCCH is CRC (cyclic redundancy check)-masked having radionetwork temporary identify (RNTI) of “A” and information about datatransmitted using a radio resource (e.g., frequency position) of “B” andtransmission format information (e.g., transport block size, modulationscheme, coding information, etc.) of “C” is transmitted through aspecific DL subframe, the UE monitors PDCCHs using RNTI information anda UE having the RNTI of “A” detects a PDCCH and receives a PDSCHindicated by “B” and “C” using information about the PDCCH.

A reference signal (RS) to be compared with a data signal is necessaryfor the UE to demodulate a signal received from the eNB. A referencesignal refers to a predetermined signal having a specific waveform,which is transmitted from the eNB to the UE or from the UE to the eNBand known to both the eNB and UE. The reference signal is also called apilot. Reference signals are categorized into a cell-specific RS sharedby all UEs in a cell and a modulation RS (DM RS) dedicated for aspecific UE. A DM RS transmitted by the eNB for demodulation of downlinkdata for a specific UE is called a UE-specific RS. Both or one of DM RSand CRS may be transmitted on downlink. When only the DM RS istransmitted without CRS, an RS for channel measurement needs to beadditionally provided because the DM RS transmitted using the sameprecoder as used for data can be used for demodulation only. Forexample, in 3GPP LTE(-A), CSI-RS corresponding to an additional RS formeasurement is transmitted to the UE such that the UE can measurechannel state information. CSI-RS is transmitted in each transmissionperiod corresponding to a plurality of subframes based on the fact thatchannel state variation with time is not large, unlike CRS transmittedper subframe.

FIG. 4 illustrates an exemplary uplink subframe structure used in 3GPPLTE/LTE-A.

Referring to FIG. 4, a UL subframe can be divided into a control regionand a data region in the frequency domain. One or more PUCCHs (physicaluplink control channels) can be allocated to the control region to carryuplink control information (UCI). One or more PUSCHs (Physical uplinkshared channels) may be allocated to the data region of the UL subframeto carry user data.

In the UL subframe, subcarriers spaced apart from a DC subcarrier areused as the control region. In other words, subcarriers corresponding toboth ends of a UL transmission bandwidth are assigned to UCItransmission. The DC subcarrier is a component remaining unused forsignal transmission and is mapped to the carrier frequency f0 duringfrequency up-conversion. A PUCCH for a UE is allocated to an RB pairbelonging to resources operating at a carrier frequency and RBsbelonging to the RB pair occupy different subcarriers in two slots.Assignment of the PUCCH in this manner is represented as frequencyhopping of an RB pair allocated to the PUCCH at a slot boundary. Whenfrequency hopping is not applied, the RB pair occupies the samesubcarrier.

The PUCCH can be used to transmit the following control information.

-   -   Scheduling Request (SR): This is information used to request a        UL-SCH resource and is transmitted using On-Off Keying (OOK)        scheme.    -   HARQ ACK/NACK: This is a response signal to a downlink data        packet on a PDSCH and indicates whether the downlink data packet        has been successfully received. A 1-bit ACK/NACK signal is        transmitted as a response to a single downlink codeword and a        2-bit ACK/NACK signal is transmitted as a response to two        downlink codewords. HARQ-ACK responses include positive ACK        (ACK), negative ACK (NACK), discontinuous transmission (DTX) and        NACK/DTX. Here, the term HARQ-ACK is used interchangeably with        the term HARQ ACK/NACK and ACK/NACK.    -   Channel State Indicator (CSI): This is feedback information        about a downlink channel. Feedback information regarding MIMO        includes a rank indicator (RI) and a precoding matrix indicator        (PMI).

The quantity of control information (UCI) that a UE can transmit througha subframe depends on the number of SC-FDMA symbols available forcontrol information transmission. The SC-FDMA symbols available forcontrol information transmission correspond to SC-FDMA symbols otherthan SC-FDMA symbols of the subframe, which are used for referencesignal transmission. In the case of a subframe in which a soundingreference signal (SRS) is configured, the last SC-FDMA symbol of thesubframe is excluded from the SC-FDMA symbols available for controlinformation transmission. A reference signal is used to detect coherenceof the PUCCH. The PUCCH supports various formats according toinformation transmitted thereon.

Table 4 shows the mapping relationship between PUCCH formats and UCI inLTE/LTE-A.

TABLE 4 Number of bits per PUCCH Modulation subframe, format schemeM_(bit) Usage Etc. 1 N/A N/A SR (Scheduling Request) 1a BPSK 1 ACK/NACKor One SR + ACK/NACK codeword 1b QPSK 2 ACK/NACK or Two SR + ACK/NACKcodeword 2 QPSK 20 CQI/PMI/RI Joint coding ACK/NACK (extended CP) 2aQPSK + BPSK 21 CQI/PMI/RI + Normal CP ACK/NACK only 2b QPSK + QPSK 22CQI/PMI/RI + Normal CP ACK/NACK only 3 QPSK 48 ACK/NACK or SR + ACK/NACKor CQI/PMI/RI + ACK/NACK

Referring to Table 4, PUCCH formats 1/1a/1b are used to transmitACK/NACK information, PUCCH format 2/2a/2b are used to carry CSI such asCQI/PMI/RI and PUCCH format 3 is used to transmit ACK/NACK information.

Reference Signal (RS)

When a packet is transmitted in a wireless communication system, signaldistortion may occur during transmission since the packet is transmittedthrough a radio channel. To correctly receive a distorted signal at areceiver, the distorted signal needs to be corrected using channelinformation. To detect channel information, a signal known to both atransmitter and the receiver is transmitted and channel information isdetected with a degree of distortion of the signal when the signal isreceived through a channel. This signal is called a pilot signal or areference signal.

When data is transmitted/received using multiple antennas, the receivercan receive a correct signal only when the receiver is aware of achannel state between each transmit antenna and each receive antenna.Accordingly, a reference signal needs to be provided per transmitantenna, more specifically, per antenna port.

Reference signals can be classified into an uplink reference signal anda downlink reference signal. In LTE, the uplink reference signalincludes:

i) a demodulation reference signal (DMRS) for channel estimation forcoherent demodulation of information transmitted through a PUSCH and aPUCCH; and

ii) a sounding reference signal (SRS) used for an eNB to measure uplinkchannel quality at a frequency of a different network.

The downlink reference signal includes:

i) a cell-specific reference signal (CRS) shared by all UEs in a cell;

ii) a UE-specific reference signal for a specific UE only;

iii) a DMRS transmitted for coherent demodulation when a PDSCH istransmitted;

iv) a channel state information reference signal (CSI-RS) for deliveringchannel state information (CSI) when a downlink DMRS is transmitted;

v) a multimedia broadcast single frequency network (MBSFN) referencesignal transmitted for coherent demodulation of a signal transmitted inMBSFN mode; and

vi) a positioning reference signal used to estimate geographic positioninformation of a UE.

Reference signals can be classified into a reference signal for channelinformation acquisition and a reference signal for data demodulation.The former needs to be transmitted in a wide band as it is used for a UEto acquire channel information on downlink transmission and received bya UE even if the UE does not receive downlink data in a specificsubframe. This reference signal is used even in a handover situation.The latter is transmitted along with a corresponding resource by an eNBwhen the eNB transmits a downlink signal and is used for a UE todemodulate data through channel measurement. This reference signal needsto be transmitted in a region in which data is transmitted.

The present invention relates to a method of providing a plurality ofdifferent services in a system by applying a different service parameteraccording to a service or a UE to satisfy a requirement of each of aplurality of the services. In particular, the present invention relatesto a method of reducing latency as much as possible by transmitting dataas soon as possible during a short time period using a short TTI(transmission time interval) for a service/UE sensitive to latency andtransmitting a response within short time in response to the data. Onthe contrary, it may transmit and receive data using a longer TTI for aservice/UE less sensitive to the latency. For a service/UE sensitive topower efficiency rather than the latency, it may repetitively transmitdata with the same lower power or transmit data using a lengthened TTI.The present invention proposes a method of transmitting controlinformation and a data signal for enabling the abovementioned operationand a multiplexing method.

For clarity, 1 ms currently used in LTE/LTE-A system is assumed as abasic TTI. A basic system is also based on LTE/LTE-A system. When adifferent service/UE is provided in a base station of LTE/LTE-A systembased on a TTI of 1 ms (i.e., a subframe length), a method oftransmitting a data/control channel having a TTI unit shorter than 1 msis proposed for a service/UE sensitive to latency. In the following, aTTI of 1 ms is referred to as a normal TTI, a TTI of a unit smaller than1 ms (e.g., 0.5 ms) is referred to as a short TTI, and a TTI of a unitlonger than 1 ms (e.g., 2 ms) is referred to as a long TTI.

First of all, a method of supporting a short TTI of a unit shorter than1 ms in a system basically using a normal TTI of 1 ms unit used inlegacy LTE/LTE-A system is described. First of all, downlink (DL) isexplained. Multiplexing between channels having a different TTI size inan eNB and an example of uplink (UL) transmission for the multiplexingare shown in FIG. 5. As a TTI is getting shorter, time taken for a UE tobuffer and decode a control channel and a data channel is gettingshorter. Time taken for performing UL transmission in response to thecontrol channel and the data channel is getting shorter. As shown in theexample of FIG. 5, in case of transmission of 1 ms TTI, when a DLchannel is transmitted in a specific n^(th) subframe, an eNB can receivea response in an (n+4)^(th) subframe in response to the DL channel. Incase of transmission of 0.5 TTI, when a DL channel is transmitted in aspecific n^(th) subframe, an eNB can receive a response in an (n+2)^(th)subframe in response to the DL channel. In particular, in order tosupport TTIs of a different length, it is necessary to support backwardcompatibility to prevent an impact on a UE operating in a legacy systemonly for DL and UL multiplexing of channels having a different TTI.

When DL/UL channels having a different length of TTI are multiplexed, itis necessary to define a method for a UE, which has received thechannels, to read a control channel and transmit/receive a data channel.A UE supporting a normal TTI only, a UE supporting a normal TTI and ashort TTI, and a UE supporting a normal TTI, a short TTI, and a long TTImay coexist in a system. In this case, when a UE supports a short TTIand a normal TTI, it means that the UE is able to receive and demodulateboth a channel transmitted with a short TTI (“short TTI channel”) and achannel transmitted with a normal TTI (“normal TTI channel”) and is ableto generate and transmit the short TTI channel and the normal TTIchannel in UL.

In a legacy LTE/LTE-A system, one subframe, i.e., a TTI, has a length of1 ms and one subframe includes two slots. One slot corresponds to 0.5ms. In case of a normal CP, one slot includes 7 OFDM symbols. A PDCCH(physical downlink control channel) is positioned at a forepart of asubframe and is transmitted over the whole band. A PDSCH (physicaldownlink shared channel) is transmitted after the PDCCH. PDSCHs of UEsare multiplexed on a frequency axis after a PDCCH section. In order fora UE to receive PDSCH of the UE, the UE should know a position to whichthe PDSCH is transmitted. Information on the position, MCS information,RS information, antenna information, information on a transmissionscheme, information on a transmission mode (TM), and the like can beobtained via the PDCCH. For clarity, PDCCH having a short TTI and PDSCHhaving a short TTI are referred to as sPDCCH and sPDSCH, respectively.If a UE receives the sPDSCH, the UE transmits HARQ-ACK via a PUCCH(physical uplink control channel) in response to the sPDSCH. In thiscase, a PUCCH having a short TTI is referred to as sPUCCH.

When it is able to configure one or a plurality of TTIs (e.g., shorterthan 1 ms) different from 1 ms TTI in a legacy LTE/LTE-A system, thepresent invention proposes a method of designing a reference signal(PUSCH DM-RS) for an uplink channel. For clarity, the present inventionconsiders a “short UL TTI” shorter than 1 ms. The short UL TTI consistsof symbols in which a data channel and a DM-RS are transmitted.

In the following description, proposal, or embodiments, such aterminology as a terminal and a UE can be used in a manner of beingmixed. However, the scope of the invention is not restricted by theterminology itself. In a broad sense, the terminal and the UE can bereferred to as a transceiver. And, in the following description,proposal, or embodiments, such a terminology as a base station and aneNB can be used in a manner of being mixed. However, the scope of theinvention is not restricted by the terminology itself. In a broad sense,the base station and the eNB can be referred to as a transceiver.

PUSCH DM-RS Design

Shared DM-RS Symbol Having a Different Cyclic Shift Between Two TTIsAdjacent to Each Other

According to legacy LTE standard, PUSCH has a transmission structurethat one DM-RS symbol per slot is transmitted in an RB. However, in caseof supporting a short UL TTI, according to a legacy DM-RS transmissionstructure, a TTI not including a DM-RS symbol may exist. On thecontrary, if a DM-RS symbol is configured in every TTI to guaranteechannel estimating/decoding performance of a PUSCH to be transmittedwith a short UL TTI, since a length of a TTI is shortened, DM-RSoverhead is rapidly increased. Hence, in order to efficiently support ashort UL TTI, it may consider a method of sharing a DM-RS in a symbolbetween two adjacent TTIs.

Specifically, when two TTIs adjacent each other transmit a DM-RS in thesame symbol (i.e., one symbol), it may be able to define a rule that thetwo TTIs differently use at least one of a base sequence and a cyclicshift. In particular, in order to provide orthogonality to a DM-RSsequence to be used in TTIs adjacent to each other, frequency bands,which are assigned to transmit PUSCH, should be the same as well. If thefrequency bands are not the same, it is unable to guaranteeorthogonality of a DM-RS sequence. And, according to the present method,it is difficult to support 1 symbol TTI. FIGS. 6, 7, 8, and 9 illustratean example of configuring a TTI within 1 ms when two TTIs adjacent toeach other transmit a DM-RS in the same symbol while using a differentcyclic shift. FIGS. 6 to 9 illustrate a case of configuring a short ULTTI of one type length. Yet, the abovementioned proposal can also beapplied to a case of configuring a short TTI of a plurality of lengths.More generally, when DM-RSs for a plurality of TTIs are transmitted inthe same SC-FDMA symbol, it is able to define a rule of differentlyusing at least one of a base sequence and a cyclic shift.

When a plurality of adjacent TTIs transmit DM-RSs in the same symbol, inorder to make a plurality of the TTIs use a different cyclic shift, itis able to inform a UE of information on a cyclic shift of a DM-RScorresponding to each PUSCH by including the information in UL grant DCIfor scheduling a PUSCH to be transmitted at each of a plurality of theTTIs. Or, it may be able to predefine a rule that a value induced from acombination of at least one selected from the group consisting of a TTIindex (e.g., even number or odd number), an RNTI of a UE, a physicallayer cell ID of an eNB, a length of a TTI, and a start symbol index ofa TTI as a cyclic shift of a DM-RS corresponding to each PUSCH.

Shared DM-RS Symbol to which a Different Comb/FDM is Applied Between TwoTTIs Adjacent to Each Other

As a different method, when two TTIs adjacent to each other transmit aDM-RS in the same symbol, it may be able to define a rule that a DM-RScorresponding to a first TTI and a DM-RS correspond to a second TTI areto be mapped to a different RE in the symbol. More generally, whenDM-RSs for a plurality of TTIs are transmitted in the same SC-FDMAsymbol, it is able to define a rule that a DM-RS corresponding to eachTTI is to be mapped to a different RE.

Specifically, when two TTIs adjacent each other transmit a DM-RS in thesame symbol, it is able to define a rule that a DM-RS signalcorresponding to a specific TTI is transmitted to in RE (i.e., evennumbered comb) corresponding to an even numbered subcarrier index in thesymbol and a DM-RS signal corresponding to the remaining TTI rather thanthe specific TTI is transmitted in an RE (i.e., odd numbered comb)corresponding to an odd numbered subcarrier index in the symbol. FIG. 10illustrates an example that a DM-RS RE for each TTI is mapped to asymbol. In FIG. 10, although a symbol between two TTIs is used for aDM-RS for the two TTIs, a symbol to which a DM-RS is allocated can berandomly designated. Among TTIs sharing a symbol to which a DM-RS isallocated, the first symbol or the last symbol can be used fortransmitting a DM-RS. This can be applied not only to FIG. 10 but alsoto all drawings.

As a further different example, it is able to define a rule that thenumber of REs in which a DM-RS signal of a TTI is transmitted isdetermined in proportion to a length of the TTI. For example, if a DM-RSfor a TTI of two adjacent symbols and a DM-RS for a TTI of four symbolsare transmitted in the same symbol, among 12 REs, the DM-RS for the TTIof two symbols is allocated to 4 REs and the DM-RS for the TTI of foursymbols can be allocated to 8 REs. This is shown in FIG. 11.

Whether a DM-RS signal corresponding to a specific TTI is transmitted inan even numbered comb or an odd numbered comb can be implicitlydetermined by a predefined rule (e.g., a first PRB index can determinethe even numbered comb or the odd numbered comb). Or, the decision canbe configured via higher layer signaling or physical layer signaling.More generally, (1) the number of REs to which a DM-RS signalcorresponding to a specific TTI is mapped among the total REs and (2)indexes of REs to which a DM-RS signal corresponding to a specific TTIis mapped can be implicitly determined by a predefined rule or can beconfigured via higher layer signaling or physical layer signaling. (1)The number of REs to which the DM-RS signal corresponding to thespecific TTI is mapped among the total REs and (2) the indexes of theREs to which the DM-RS signal corresponding to the specific TTI ismapped can be independently configured according to a DM-RS symbolshared by a plurality of TTIs adjacent to each other.

As mentioned in the foregoing description, when DM-RSs for a pluralityof TTIs are transmitted in the same SC-FDMA symbol, if a DM-RScorresponding to each TTI is mapped to a different RE, PUSCH transmitpower and DM-RS transmit power can be differently configured. The DM-RStransmit power may use a value indicated to a UE via higher layersignaling/physical layer signaling or a value derived from the PUSCHtransmit power according to a predefined rule.

PHICH Resource Determination

According to current LTE standard, a PHICH resource index is determinedby a first PRB index assigned for PUSCH and a DM-RS cyclic shift. Whencomb-based multiplexing is introduced, if HARQ management using PHICH isconsidered, the PHICH resource index can be determined not only by thefirst PRB index and the DM-RS cyclic shift but also by combindex-related information (e.g., even number/odd number, first DM-RS RE,etc.) and/or number of DM-RS REs per 1 PRB, and the like.

Dynamic Switching

If a frequency resource allocated to transmit PUSCH corresponds to thesame TTIs adjacent to each other, as mentioned in the foregoingdescription, although DM-RSs are transmitted, it is able to maintainorthogonality between the DM-RSs. However, since UL resource allocationmay be dynamically changed in every TTI, a frequency resource allocationsize for PUSCH may be the same or different between TTIs adjacent toeach other. In particular, if a resource allocation size for PUSCH isdifferent between TTIs adjacent to each other, it may be moreappropriate to apply a different comb/FDM to the two TTIs adjacent toeach other. In particular, if it is able to use the abovementionedmethods by dynamically switching the methods according to scheduling ofan eNB, it is more preferable. To this end, when DM-RSs for a pluralityof TTIs are transmitted in the same symbol, it may be able to inform aUE of detail information (e.g., cyclic shift, comb information, etc.) onwhether a DM-RS for a specific TTI is mapped to the total REs of asymbol or an RE corresponding to a specific comb via physical layersignaling. The information indicated via the physical layer signalingcan be independently (differently) defined/configured according to a TTIlength. As a specific example, a legacy specific field (e.g., DM-RScyclic shift field) included in a UL grant for scheduling PUSCHtransmission or a new field can be defined to include informationdescribed in the following.

TABLE 5 cyclic shift field in UL grant DCI Description 000 even comb(n_(DMRS,λ) ⁽²⁾ = a) 001 odd comb (n_(DMRS,λ) ⁽²⁾ = b) 010 n_(DMRS,λ)⁽²⁾ = c . . . 111 n_(DMRS,λ) ⁽²⁾ = h Note: a = b = 0, or a = 0, b = 6,or a = 6, b = 0 can be configured. c to h can be configured by adifferent value.

Shared DM-RS Having a DM-RS Frequency Resource Identically ConfiguredBetween Two TTIs Adjacent to Each Other

According to current LTE standard, a base sequence for generating aPUSCH DM-RS sequence is differently configured according to UL resourceallocation. As mentioned in the foregoing description, when two TTIstransmit DM-RSs in the same symbol, in order to secure orthogonalitybetween two DM-RSs using a different cyclic shift, a resource allocationsize for PUSCH to be transmitted to two TTIs should be the same.However, since UL resource allocation can be dynamically changed inevery TTI, a frequency resource allocation size may be the same ordifferent between TTIs adjacent to each other. Hence, when two TTIsadjacent to each other transmit DM-RSs in the same symbol, it may beable to allocate a DM-RS transmission resource to a UE irrespective of aresource for transmitting PUSCH and the UE can transmit the PUSCH andthe DM-RS using a different UL resource. More generally, when DM-RSs fora plurality of TTIs are transmitted in the same SC-FDMA symbol, a DM-RStransmission resource can be allocated to each TTI irrespective of aresource allocated to transmit PUSCH. Hence, a UE is able to transmitPUSCH and a DM-RS using a different UL resource.

In this case, a UL resource for transmitting the DM-RS allocates acommon frequency resource to a plurality of TTIs and may differently useat least one of a base sequence and a cyclic shift. For example, asshown in FIG. 12, if a UL resource for transmitting a DM-RS allocates acommon frequency resource to two TTIs adjacent to each other, uses thesame base sequence, and uses a different cyclic shift, although a sizeof a PUSCH resource allocated to the two TTIs adjacent to each other isdifferent, it is able to secure orthogonality between DM-RSs transmittedin the same symbol. And, in order to efficiently demodulate PUSCH, aDM-RS transmission resource can be allocated in a manner of being equalto or greater than a PUSCH transmission resource.

In this case, the UL resource for transmitting the DM-RS can bedetermined by the specific number of RBs (e.g., a part of the whole ULfrequency band) determined in advance, the number of RBs dynamicallyindicated by an eNB, or the whole UL frequency band irrespective of a ULresource allocated for PUSCH. Or, if the UL resource allocated for PUSCHcorresponds to X RB and the UL resource for transmitting the DM-RScorresponds to Y RB, Y=N*X is satisfied. In this case, the N can beconfigured by an integer promised/defined in advance or an integersignaled via higher layer signaling/physical layer signaling. Or, when apart of the total system bandwidth is configured for a specific TTIlength, the whole frequency resource among the partial resource, aresource as much as RBs of a promised/predefined size, or a resource asmuch as RBs signaled via higher layer/physical layer signaling can bedefined for the specific TTI length.

In order to support the method above, the eNB can provide the UE withinformation on resource allocation of a DM-RS to be transmitted by theUE via higher layer signaling. Or, the eNB can provide the UE withinformation on resource allocation of a DM-RS to be transmitted by theUE via a legacy specific field in UL grant DCI for scheduling PUSCHtransmission or a new field. Or, resource allocation of a DM-RS can bedetermined according to a predefined rule irrespective of a UL resourceallocated for PUSCH.

Hopping/Interlacing

More generally, a PUSCH transmission resource and a DM-RS transmissionresource can be differently configured in a specific TTI. In this case,the DM-RS transmission resource can be allocated in a manner of beingequal to or greater than the PUSCH transmission resource. Preferably, itis able to allocate the DM-RS transmission resource greater than thePUSCH transmission resource. By doing so, when DM-RSs for a plurality ofTTIs are transmitted in the same symbol, it is able to support hoppingof the PUSCH transmission resource within a TTI.

It is able to define a rule that a PUSCH transmission resource is to bechanged according to a predefined time unit (e.g., 1 symbol) or a timeunit as much as predetermined time according to a TTI length within aspecific TTI. In this case, a resource for transmitting PUSCH can berestricted to a predetermined DM-RS transmission resource region. And, ahopping pattern for the PUSCH transmission resource within a specificTTI can be promised/defined in advance or can be signaled to a UE viahigher layer signaling or physical layer signaling.

If a short TTI is introduced, coverage of a sPUSCH can be reduced. Inthis case, if the PUSCH transmission resource hops within a TTI, it mayexpect an effect of enhancing reliability with the help of a frequencydiversity gain.

Comb-Type DM-RS without Shared DM-RS Symbol

When a plurality of TTIs transmit DM-RS in the same symbol and it isnecessary to secure orthogonality between two DM-RSs using a differentcyclic shift, there may exist a constraint that resource allocationsizes for PUSCH to be transmitted at the TTIs to be the same. Or, it isable to secure orthogonality using the same base sequence in an RB unitto avoid the constraint. Yet, this may cause excessive increase of PARR(peak to average power ratio). Hence, it may consider transmitting acomb-type DM-RS for each TTI without sharing a DM-RS in a symbol betweena plurality of TTIs. In this case, if a TTI length increases, it may beable to configure the number of REs used for transmitting a DM-RScompared to the total REs to be increased in proportion to the increaseof the TTI length. Specifically, “number of REs used for transmitting aDM-RS among the N number of REs within a TTI” can be defined in advanceor can be provided to a UE via higher layer signaling or physical layersignaling. In this case, the N can be defined by ‘the number ofsubcarriers corresponding to 1 resource block (i.e., 12)*the number ofsymbols corresponding to a TTI length’. Or, a ratio of REs used fortransmitting a DM-RS to the N number of REs within a TTI can be definedin advance or can be provided to a UE via higher layer signaling orphysical layer signaling. Or, the number of REs/ratio of REs used fortransmitting a DM-RS during time duration corresponding to a pluralityof TTIs can be defined in advance or can be provided to a UE via higherlayer signaling or physical layer signaling.

“The number of REs used for transmitting a DM-RS among the N number ofREs within a TTI” or “the ratio of REs used for transmitting a DM-RS tothe N number of REs within a TTI” can be independently (differently)configured for a plurality of TTIs corresponding to determined timeduration (e.g., 1 ms).

When a comb-type DM-RS is transmitted, RE mapping can be defined inadvance or can be provided to a UE via higher layer signaling orphysical layer signaling. When RE mapping is performed on the comb-typeDM-RS proposed in the present invention, it is apparent that the REmapping is applied irrespective of a DM-RS symbol shared by adjacentTTIs. When the comb-type DM-RS is transmitted, the RE mapping can beperformed as follows.

Option 1: DM-RS RE Mapping Configuration According to TTI Length

It may be able to configure unique DM-RS RE mapping according to a TTIlength. For example, when a TTI length corresponds to 1, 2, 3, and 4symbols, the number of DM-RS REs 2, 4, 6, and 8 can be set to a UE.DM-RS RE mapping can be defined as FIG. 13. The DM-RS RE mapping can beexpressed by an equation described in the following.

a_(k,l) ^((p)): complex-valued modulation symbols. k corresponds to asubcarrier index and l corresponds to a symbol index.

k = 6m^(′) + N_(sc)^(RB)n_(PRB) + k^(′)$k^{\prime} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} l\mspace{14mu} {mod}\mspace{14mu} 2} = 0} \\3 & {{{if}\mspace{14mu} l\mspace{14mu} {mod}\mspace{14mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1} \right.$

Option 2: DM-RS RE Mapping According to Resource of Short TTI

It may be able to define a rule that DM-RS RE mapping is to be changedaccording to a position of a TTI. Specifically, it is able to define arule that DM-RE RE mapping is to be changed according to a position of aTTI within specific time (e.g., 1 ms). In this case, the position of theTTI can be regulated by a starting symbol or an ending symbol of theTTI, a TTI index, or a specific symbol determined by a predeterminedrule. When a UE is scheduled at a plurality of TTIs during specific timeduration, a network may use a DM-RS of a different TTI to performchannel estimation and decoding on a specific TTI by utilizing differentDM-RS RE mapping of each TTI.

For example, when a length of TTI #n and a length of TTI #n+1 areconfigured by 1 symbol and 2 symbols, respectively, and PUSCH iscontinuously scheduled to a UE at the two TTIs, DM-RS RE mapping shownin the right drawing of FIG. 14 can be more efficient in estimating achannel compared to DM-RS RE mapping shown in the left drawing of FIG.14. In this case, it may be able to define a rule that a DM-RS for1-symbol TTI is to be mapped to a subcarrier index {3, 9} rather than{0, 6}. Or, relevant information can be provided to a UE via higherlayer signaling or physical layer signaling.

As a different example, it may be able to define DM-RS RE mapping to beperformed during specific time duration (e.g., 1 ms) in advance. In thiscase, it is able to define a rule that a UE transmits only a DM-RSmapped to a symbol corresponding to a TTI configured to transmit PUSCH.FIG. 15 illustrates an example of the rule.

As a further different example, it may be able to define a rule that REmapping is to be shifted at every TTI as much as a promised subcarrierindex.

As a further different example, it may be able to define a rule thatseparate DM-RS RE mapping is to be applied according to a frequencyresource such as an RB index or the like.

Although the abovementioned options have proposed comb-type DM-RS REmapping of a staggered form to make DM-RS REs to be evenly distributedto symbols/subcarriers within a specific TTI, the proposed rules can begenerally applied to RE mapping (e.g., RE mapping of which more DM-RSREs are defined in a specific symbol) rather than the DM-RS RE mappingof the staggered form.

DM-RS on/Off

When a DM-RS is transmitted at every TTI, if a TTI of a short length(e.g., 1 symbol TTI) is configured, it may cause excessive DM-RSoverhead. Hence, it may be able to define a rule that a UE transmitsDM-RS during the determined number of TTIs only from among specific timeduration corresponding to a plurality of TTIs. For example, it may beable to configure the UE to transmit DM-RS during M (M<K) number of TTIsonly from among time duration corresponding to K number of TTIs. In thiscase, the number of TTIs during which the DM-RS is transmitted can bedefined/promised in advance or can be provided to a UE via higher layersignaling or physical layer signaling.

In order to reduce blind detection of a network, it may be able toconfigure DM-RS to be transmitted at a predefined TTI or a TTI ofsignaled timing only among specific time duration corresponding to aplurality of TTIs.

Or, it may be able to configure a UE to transmit a DM-RS to a determinedSC-FDMA symbol only from among specific time duration corresponding to aplurality of TTIs. In this case, an index of the SC-FDMA symbol to whichthe DM-RS is to be transmitted can be defined/promised in advance or canbe provided to a UE via higher layer signaling or physical layersignaling.

Regarding each DM-RS or a plurality of DM-RSs to be transmitted duringthe time duration, it is able to inform a UE of all or a part ofinformation on whether or not a DM-RS is mapped to the entire REs in asymbol, information on whether or not a DM-RS is mapped to an REcorresponding to a specific comb, a DM-RS cyclic shift, an OCC(orthogonal cover code), and comb pattern information via higher layersignaling or physical layer signaling. In this case, specifically, thephysical layer signaling may correspond to (1) UL grant DCI thatschedules a plurality of TTIs, (2) UL grant DCI that schedules one ormore TTIs defined/promised in advance among a plurality of the TTIs, or(3) a specific DCI type (slow/first DCI or fast/second DCI) of two-levelDCI.

In this case, the two-level DCI corresponds to DCI which is consideredat the time of introducing a sTTI. The slow/first DCI corresponds to DCIwhich is transmitted at the first sTTI only of every subframe and thefast/second DCI corresponds to DCI which is transmitted at every sTTI.Compared to the fast/second DCI, the slow/first DCI carries more staticinformation. The fast/second DCI can carry more dynamic information.

Or, a plurality of TTIs can be configured as candidates for a TTI atwhich a DM-RS is to be transmitted among specific time duration. A UEcan be configured to transmit a DM-RS for a part of the candidates.

If the TTI at which the DM-RS is to be transmitted is not UL scheduled,PUSCH data can be transmitted only without transmitting the DM-RS duringthe specific time duration. This is not preferable. In order to preventthe abovementioned case, among the specific time duration correspondingto a plurality of the TTIs, the TTI at which the DM-RS is to betransmitted can be restricted to the first TTI accompanied with PUSCHscheduling.

Collision Between DM-RS and SRS

According to LTE standard, the last SC-FDMA symbol of 1 ms UL subframecan be used for transmitting an SRS. If a short TTI is introduced,according to the aforementioned proposals, a DM-RS symbol can becollided with an SRS symbol in the same symbol.

If a DM-RS for a short TTI and an SRS are configured or promised not tobe transmitted at the same time in a specific SC-FDMA symbol, it is ableto define a rule that the SRS is to be dropped and the DM-RS is to betransmitted only in the specific SC-FDMA symbol. In this case, the SRSmay correspond to a legacy SRS or a new SRS newly introduced for a shortTTI. Or, a priority of the SRS and a priority of the DM-RS can bedetermined according to a symbol index to determine a type of an RS tobe dropped. The abovementioned rule can be differently defined accordingto whether an SRS corresponds to a periodic SRS or an aperiodic SRS.

Shared DM-RS for a UE which is Scheduled During Two Consecutive TTIs

When a plurality of TTIs are configured to transmit a DM-RS in the samesymbol, if a plurality of the TTIs are PUSCH scheduled to a UE, it maybe difficult for the UE to transmit a DM-RS by differently using a basesequence, a cyclic shift, or a comb pattern. In particular, if aplurality of the TTIs, which are configured to transmit a DM-RS in thesame symbol, are PUSCH scheduled to the UE, it is necessary to have amethod of transmitting a DM-RS. In the following, a method oftransmitting a DM-RS is described in more detail.

-   -   Option 1: When a UE transmits a DM-RS in a corresponding symbol,        the UE can transmit the DM-RS using a cyclic shift indicated by        a UL grant corresponding to PUSCH transmission scheduled at a        TTI (e.g., odd numbered or even numbered TTI) which is        determined according to a predefined rule and/or a base sequence        generated according to a UL resource scheduled at a TTI which is        determined according to a predefined rule. Or, when a UE        transmits a DM-RS in a corresponding symbol, the UE can transmit        the DM-RS using a cyclic shift indicated by a UL grant        corresponding to a PUSCH transmission scheduled at a specific        TTI configured/indicated via higher layer signaling or physical        layer signaling and/or a base sequence generated according to a        UL resource scheduled at a specific TTI.    -   Option 1-a: When a UE transmits a DM-RS in a corresponding        symbol, the UE maps/transmits the DM-RS using a comb indicated        by a UL grant corresponding to a PUSCH transmission scheduled at        a TTI which is determined according to a predefined rule. Or,        the UE maps/transmits the DM-RS using a comb implicitly        determined for a TTI which is determined according to a        predefined rule or a comb configured via higher layer signaling        for a TTI which is determined according to a predefined rule.    -   Option 1-b: When a UE transmits a DM-RS in a corresponding        symbol, the UE maps/transmits the DM-RS using a comb indicated        by UL grant DCI corresponding to a PUSCH transmission scheduled        at a specific TTU which is configured/indicated via higher layer        signaling or physical layer signaling. Or, the UE maps/transmits        the DM-RS using a comb implicitly determined for a specific TTI        which is configured/indicated via higher layer signaling or        physical layer signaling or a comb configured by higher layer        signaling for a specific TTI which is configured/indicated via        higher layer signaling or physical layer signaling.    -   Option 2: When a UE transmits a DM-RS in a corresponding symbol,        the UE can transmit the DM-RS using a cyclic shift indicated by        UL grant DCI corresponding to a PUSCH transmission to which a        bigger UL resource is allocated among PUSCHs scheduled at a        plurality of TTIs and/or a base sequence which is generated        according to a bigger UL resource. If PUSCH resources scheduled        at a plurality of the TTIs are the same, the UE can transmit the        DM-RS using a cyclic shift indicated by UL grant DCI        corresponding to a PUSCH transmission scheduled at a TTI (e.g.,        odd numbered TTI or even numbered TTI) which is determined        according to a predefined rule. Or, if PUSCH resources scheduled        at a plurality of the TTIs are the same, the UE can transmit the        DM-RS using a cyclic shift indicated by UL grant DCI        corresponding to a PUSCH transmission scheduled at a specific        TTI which is configured/indicated via higher layer signaling or        physical layer signaling and/or a base sequence which is        generated according to a UL resource scheduled at a specific TTI        while transmitting the DM-RS in a corresponding symbol.    -   Option 2-a: When a UE transmits a DM-RS in a corresponding        symbol, the UE can map/transmit the DM-RS using (1) a comb        indicated by UL grant DCI corresponding to a PUSCH transmission        to which a bigger UL resource is allocated among PUSCHs        scheduled at a plurality of TTIs, (2) a comb implicitly        determined for a TTI to which a bigger UL resource is allocated        among PUSCHs scheduled at a plurality of TTIs, or (3) a comb        configured by higher layer signaling for a TTI to which a bigger        UL resource is allocated among PUSCHs scheduled at a plurality        of TTIs.    -   Option 3: When a plurality of TTIs are continuously PUSCH        scheduled to a UE, it may be able to define a rule that the UE        follows a specific cyclic shift value which is specified from a        plurality of values indicated by a plurality of UL grant DCI        corresponding to a plurality of the TTIs and ignores the        remaining values. Or, when a plurality of TTIs are continuously        PUSCH scheduled to a UE, it may be able to define a rule that        the UE follows a specific cyclic shift value        configured/indicated via higher layer signaling. The rule can be        applied only when UL resources scheduled at a plurality of the        TTIs are the same or a part of the UL resources is overlapped.    -   Option 4: When DM-RSs for a plurality of TTIs are transmitted in        the same symbol and a DM-RS corresponding to each TTI is        configured to be mapped to a different RE, a UE maps/transmit        the DM-RS to the whole of the symbol without applying a comb. In        this case, a value indicated by UL grant DCI on PUSCH, which is        scheduled at a predetermined TTI, a predetermined specific        cyclic shift value, or a specific cyclic shift value which is        configured in advance via higher layer signal can be used as a        cyclic shift value.    -   Option 4-1: More generally, when a plurality of TTIs are        continuously PUSCH scheduled to a UE and DM-RSs for a plurality        of the TTIs are transmitted in a manner of being mapped to a        different frequency resource (e.g., RE) in the same symbol        (e.g., using an odd numbered comb type or an even numbered comb        type), a rule/method for the UE to transmit a DM-RS is described        in the following in detail.    -   Method 1: A DM-RS sequence can be transmitted in a manner of        being mapped to a frequency resource corresponding to the entire        PRBs which are allocated to perform PUSCH scheduling in a DM-RS        symbol. In this case, a cyclic shift value included in UL grant        DCI for PUSCH which is scheduled at a predetermined TTI, a        cyclic shift value included in UL grant DCI in case of multi-TTI        scheduling, a cyclic shift value included in slow DCI (or fast        DCI for a predetermined or signaled TTI) in case of two-level        DCI, a predetermined specific cyclic shift value, a specific        cyclic shift value configured in advance via higher layer        signaling, and the like can be used as a cyclic shift of a DM-RS        (in particular, when a cyclic shift value included in UL grant        DCI, which schedules a plurality of the TTIs, indicates a        different value).    -   Method 2: When a specific field value, which is included in UL        grant DCI scheduling a plurality of TTIs, indicates a different        DM-RS transmission scheme or implicitly indicates a different        DM-RS transmission scheme, a DM-RS transmission scheme in a        corresponding DM-RS symbol can be determined from among a        predefined specific DM-RS transmission scheme, a DM-RS        transmission scheme indicated by UL grant DCI on PUSCH scheduled        by a predetermined TTI, in case of multi-TTI scheduling, a DM-RS        transmission scheme indicated by corresponding UL grant DCI, in        case of two-level DCI, a DM-RS transmission scheme indicated by        slow DCI (or fast DCI for a predetermined or signaled TTI), a        predetermined specific DM-RS transmission scheme, and a specific        DM-RS transmission scheme configured in advance via higher layer        signaling. The abovementioned UE operation can be identically        applied irrespective of a specific field value included in UL        grant DCI that implicitly indicates a different DM-RS        transmission scheme. In this case, the DM-RS transmission scheme        can include information indicating whether a DM-RS sequence is        mapped to a frequency resource corresponding to the entire PRBs,        which are allocated to perform PUSCH scheduling, or a specific        frequency resource only similar to a comb-type (with or without        power boosting).    -   Method 3-1: When a specific field value, which is included in UL        grant DCI scheduling a plurality of TTIs, indicates a different        DM-RS transmission scheme, it may be able to define a rule that        a DM-RS sequence is transmitted in a manner of being mapped to a        frequency resource corresponding to the entire PRBs, which are        allocated to perform PUSCH scheduling. If the specific field        value indicates the same DM-RS transmission scheme, similar to a        comb-type, it may be able to define a rule that a DM-RS sequence        is transmitted in a manner of being mapped to a specific        frequency resource only.    -   Method 3-2: On the contrary, when a specific field value, which        is included in UL grant DCI scheduling a plurality of TTIs,        indicates a different DM-RS transmission scheme, similar to a        comb-type, it may be able to define a rule that a DM-RS sequence        is transmitted in a manner of being mapped to a specific        frequency resource only. If the specific field value indicates        the same DM-RS transmission scheme, it may be able to define a        rule that a DM-RS sequence is transmitted in a manner of being        mapped to a frequency resource corresponding to the entire PRBs,        which are allocated to perform PUSCH scheduling.    -   Option 5: When a plurality of TTIs are continuously PUSCH        scheduled to a UE, if a plurality of UL grant DCI corresponding        to a plurality of the TTIs indicate the UE to use a different        comb-type (or comb-pattern), it may be able to define a rule        that the UE transmits a DM-RS sequence to the whole REs of a        DM-RS symbol using a specific cyclic shift/base sequence to        avoid the increase of PAPR. In this case, the cyclic shift/base        sequence can be determined by UL grant DCI on a        predefined/promised TTI. Or, it may use a separately configured        cyclic shift/base sequence or a cyclic shift/base sequence        configured via higher layer signaling. The abovementioned        operation of the UE can be performed only when the operation is        indicated via higher layer signaling/physical layer signaling.    -   Option 6: When a plurality of TTIs are continuously PUSCH        scheduled to a UE, if a plurality of UL grant DCI corresponding        to a plurality of the TTIs indicate the UE to use a different        DM-RS mapping structure (e.g., one UL grant DCI indicates the UE        to transmit a DM-RS by mapping the DM-RS to the entire REs of a        symbol and another UL grant DCI indicates the UE to transmit a        DM-RS by mapping the DM-RS to an RE corresponding to a specific        comb-pattern), the UE can transmit the DM-RS using a cyclic        shift indicated by UL grant DCI corresponding to a PUSCH        transmission scheduled at a specific TTI, which is determined        according to a predefined rule, and/or a base sequence which is        generated according to a UL resource scheduled at the TTI. Or,        if a plurality of UL grant DCI indicate the UE to use a        different DM-RS mapping structure, the UE can transmit a DM-RS        using a cyclic shift indicated by UL grant DCI corresponding to        a PUSCH transmission scheduled at a specific TTI, which is        configured/indicated via higher layer signaling or physical        layer signaling, and/or a base sequence which is generated        according to a UL resource scheduled at the specific TTI. Or, if        a plurality of UL grant DCI indicate the UE to use a different        DM-RS mapping structure, the UE can transmit a DM-RS by mapping        the DM-RS to the entire REs using a cyclic shift indicated by UL        grant DCI, which indicates the DM-RS to be always transmitted in        a manner of being mapped to the entire REs, and/or a base        sequence which is generated according to a UL resource scheduled        at a specific TTI. Or, if a plurality of UL grant DCI indicate        the UE to use a different DM-RS mapping structure, the UE can        transmit a DM-RS by mapping the DM-RS to the entire REs of a        symbol using a cyclic shift/base sequence which is configured        via higher layer signaling.    -   Option 7: When a plurality of TTIs are continuously PUSCH        scheduled to a UE, the UE may not expect that a plurality of UL        grant DCI corresponding to a plurality of the TTIs indicate the        UE to use a different DM-RS mapping structure (e.g., one UL        grant DCI indicates the UE to transmit a DM-RS by mapping the        DM-RS to the entire REs of a symbol and another UL grant DCI        indicates the UE to transmit a DM-RS by mapping the DM-RS to an        RE corresponding to a specific comb-pattern). Similarly, the UE        may not expect that a plurality of UL grant DCI corresponding to        a plurality of the TTIs indicate a different cyclic shift. In        the situation above, if a different DM-RS mapping structure or a        different cyclic shift is indicated via a plurality of the UL        grant DCI, the UE can drop the entire PUSCH scheduled at a        corresponding TTI or a part of the PUSCH.    -   Option 7-1: A UE does not expect that an RA (resource        allocation) field value included in UL grant DCI, which        schedules a plurality of TTIs, indicates a different PUSCH        resource allocation. If a different PUSCH resource allocation is        indicated, it may be able to define a rule that the UE performs        transmission on a specific TTI corresponding to retransmission        only among TTIs including a TTI to which a predetermined or a        bigger resource is allocated, a preceding TTI in time, the last        TTI in time, and a plurality of TTIs corresponding to initial        transmission and retransmission. Or, the UE may drop all of a        plurality of the TTIs.

Power Control for Shared DM-RS Symbol

When a plurality of TTIs transmit DM-RSs in the same symbol and aplurality of the TTIs are scheduled to a UE, if PUSCH transmit powercorresponding to two TTIs is differently configured, transmit power of aDM-RS symbol may become ambiguous. When a plurality of TTIs arescheduled to a UE, a method of configuring transmit power of a DM-RSsymbol is described in the following in detail.

-   -   Option 1: Transmit power of a DM-RS symbol can be determined        according to transmit power set to PUSCH corresponding to a TTI,        which is determined according to a predefined rule, or a        specific TTI configured/indicated via higher layer signaling or        physical layer signaling.    -   Option 2: Transmit power of a DM-RS symbol can be determined        according to transmit power set to PUSCH corresponding to a TTI        to which a bigger UL resource is allocated to transmit the        PUSCH.    -   Option 3: When a plurality of TTIs transmit DM-RSs in the same        symbol, it may be able to define a rule that a plurality of the        TTIs follow a specific transmit power value configured/indicated        via higher layer signaling. Or, it may be able to define a rule        that a plurality of the TTIs follow a transmit power value        determined by a specific parameter which is configured/indicated        via higher layer signaling.

More generally, when DM-RSs for a plurality of TTIs are transmitted inthe same symbol and a plurality of the TTIs are scheduled to a UE, amethod of performing power control is proposed in the following.

-   -   Option 1: When DM-RSs for a plurality of TTIs are configured to        be transmitted in the same symbol and a plurality of the TTIs        are scheduled to a UE, transmit power for a plurality of the        TTIs can be determined by UL grant DCI that schedules a specific        TTI (e.g., first TTI) among a plurality of the TTIs. More        specifically, transmit power of a UE can be determined by a TPC        (transmit power control) field included in UL grant DCI. In this        case, the remaining UL grant DCI may exist except specific UL        grant DCI, which is used for determining the transmit power. A        transmit power-related parameter (e.g., TPC field) included in        the remaining UL grant DCI can be ignored. When a plurality of        contiguous TTIs are scheduled to a UE, “the rule of determining        the transmit power of a plurality of the TTIs using the UL grant        DCI that schedules the specific TTI (e.g., first TTI)” is        applied during specific time duration only. In this case, the        specific time duration can be defined in advance (e.g., 1 ms),        can be signaled via physical layer signaling, or can be        configured via higher layer signaling. And, transmit power for        time duration appearing after the specific time duration can be        determined by a specific field (e.g., TPC) included in UL grant        DCI that schedules a specific TTI (e.g., a first TTI appearing        after the specific time duration) appearing after the specific        time duration.    -   Option 2: When DM-RSs for a plurality of TTIs are configured to        be transmitted in the same symbol and a plurality of the TTIs        are scheduled to a UE, transmit power for a plurality of the        TTIs can be determined by specific UL grant DCI. Specifically,        the specific UL grant DCI may correspond to (1) UL grant DCI        that schedules one or more TTIs defined/promised in advance        among a plurality of the TTIs or (2) a specific DCI type        (slow/first DCI or fast/second DCI) of two-level DCI.        Specifically, transmit power of the UE can be determined by a        TPC field included in the specific UL grant DCI. In this case,        the remaining UL grant DCI may exist except the specific UL        grant DCI, which is used for determining the transmit power. A        transmit power-related parameter (e.g., TPC field) included in        the remaining UL grant DCI can be ignored. It may be able to        define a rule that the power configuration method is to be        applied to a scheduling target TTI of specific UL grant DCI        performing multi-TTI scheduling only or a target TTI which is        scheduled by a specific type (slow/first DCI or fast/second DCI)        of two-level DCI only. Or, it may be able to define a rule that        transmit power of all TTIs, which are scheduled during specific        time duration (e.g., 1 ms), is to be determined by a TPC field        of a first UL grant DCI of the time duration.

In particular, transmit power of a UE is restricted by a field value ofa specific DCI field. This is aimed for securing efficiency of ULtransmission by minimizing a change of the transmit power of the UE. Ifthe transmit power of the UE changes according to a TTI, a ratiooccupied by a power transition section of a transmitter of the UE or apower amplifier related to the transmitter increases, therebydeteriorating the efficiency of the transmitter.

Moreover, as mentioned in the foregoing description, when DM-RSs for aplurality of TTIs are transmitted in the same symbol, if a DM-RStransmission resource is allocated to a UE irrespective of a resourcefor transmitting PUSCH, DM-RS transmit power can be set to the UE viahigher layer signaling or physical layer signaling irrespective of PUSCHtransmit power. Or, it may be able to define a rule that the UE followsa DM-RS transmit power value determined by a separate parameterconfigured/indicated by higher layer signaling.

-   -   According to current LTE standard, a base sequence for        generating a DM-RS sequence is determined according to a size of        a scheduled PUSCH RB. According to a part of the aforementioned        proposals, it may be necessary to generate a sequence of a short        length, which is not defined in the current LTE standard        operation. For example, when it is defined as an RS is to be        mapped to a partial RE only of an SC-FDMA symbol of an RB, if 1        RB is scheduled using PUSCH, ambiguity may occur in generating a        sequence. Although X (X>=1) RB is allocated, since a length of a        sequence to be actually generated does not correspond to X*12        subcarriers, it is not matched with the current standard.

If RE mapping is defined in a UE in a manner that an RS is mapped toM_RE number of REs only among 12 REs of an SC-FDMA symbol of an RB, theUE may expect that X RB is scheduled by PUSCH to satisfy M_RE*X>=Y(where, Y corresponds to a predefined specific natural number, forexample, Y=36 or 12). Or, the UE may expect that X RB is scheduled byPUSCH to satisfy M_RE*X<36 and M_RE*X=12 or 24. If RBs not satisfyingthe M_RE*X>=Y are scheduled by PUSCH, the UE can drop the PUSCH.

Or, it may be able to define a rule that PUSCH is to be scheduled to aUE by defining a scheduling unit in a unit of {12/M_RE}. For example, ifRE mapping is defined in a manner that an RS is mapped to 6 REs among 12REs of an SC-FDMA symbol of an RB, PUSCH can be scheduled in a unit of{12/6}=2 RBs.

In the foregoing description, an example that an SC-FDMA symbol of an RBis configured by 12 REs has been explained. The present invention canalso be applied to a case that an SC-FDMA symbol of an RB is configuredby the different number of REs.

-   -   As a further different proposal, when DM-RSs for a plurality of        TTIs are transmitted in an SC-FDMA symbol of the same position        or a DM-RS for a TTI is transmitted in a specific symbol        belonging to the TTI or a specific symbol not belonging to the        TTI, a DM-RS structure can be defined/promised in advance or can        be signaled to a UE via higher layer signaling or physical layer        signaling. A rule for the DM-RS structure can be applied during        specific time duration. In this case, the specific time duration        can also be defined/promised in advance or signaled. The        specific time duration can be independently (differently)        defined/promised according to a TTI length or can be signaled to        the UE via higher layer signaling or physical layer signaling.

The UE can report information on a DM-RS structure capable of beingsupported by the UE to a base station. Or, the UE can report informationon a DM-RS structure capable of being supported by the UE according to aTTI length.

-   -   As a further different proposal, when DM-RSs for a plurality of        TTIs are transmitted in an SC-FDMA symbol of the same position,        it may be able to define a rule that a DM-RS for a TTI is to be        additionally transmitted in one or more symbols within an        individual TTI irrespective of the SC-FDMA symbol. Whether to        apply the rule can be determined according to a TTI length. Or,        whether to apply the rule can be determined according to a        network configuration via higher layer/physical layer signaling.        Specifically, the rule can be applied to a TTI for transmitting        PUCCH including HARQ-ACK. FIG. 16 illustrates an example of the        abovementioned proposal.

It may be able to define a rule that the same cyclic shift, a value towhich a predefined/predetermined offset is added, or a cyclic shiftconfigured via higher layer/physical layer signaling is to be used by anadditionally transmitted DM-RS and a DM-RS transmitted in a symbolshared by a plurality of TTIs.

It may be able to define a rule that (1) the number of symbols in whichthe additionally transmitted DM-RS is transmitted within an individualTTI and (2) symbols in which the additionally transmitted DM-RS istransmitted within an individual TTI are to be defined/promised inadvance or are to be determined by a configuration of a network viahigher layer/physical layer signaling.

And, (1) the number of symbols in which the additionally transmittedDM-RS is transmitted within an individual TTI and (2) symbols in whichthe additionally transmitted DM-RS is transmitted within an individualTTI can be differently configured according to a TTI length.

DM-RS on/Off by Multi-TTI Scheduling

When a plurality of UL data channels for a plurality of TTIs arescheduled by single UL grant DCI, it may be able to define a rule that aDM-RS is to be transmitted at TTIs as many as TTIs determined duringspecific time duration corresponding to a plurality of scheduled TTIs ora TTI of determined timing only. The number/timing of TTIs at which aDM-RS is to be transmitted can be defined/promised in advance or can beindicated by higher layer signaling or the UL grant DCI.

In this case, all or a part of information on whether a DM-RS or aplurality of DM-RSs to be transmitted during the time duration aretransmitted in a manner of being mapped to the entire REs of a symbol oran RE corresponding to a specific comb, a DM-RS cyclic shift, an OCC,and comb-pattern information can be indicated to a UE via higher layersignaling or physical layer signaling. In this case, specifically, thephysical layer signaling may correspond to UL grant DCI that schedules aplurality of the UL data channels.

When PUSCHs for a plurality of TTIs are scheduled by single UL grantDCI, it may be able to define a rule that a DM-RS is to be transmittedin an SC-FDMA symbol only which is determined within specific timeduration corresponding to a plurality of scheduled TTIs. An index of theSC-FDMA symbol in which the DM-RS is to be transmitted can bedefined/promised in advance or can be indicated by higher layersignaling or the UL grant DCI. For example, the index of the SC-FDMAsymbol in which the DM-RS is to be transmitted can be differently (oridentically) defined/promised according to the number of TTIs at whichthe DM-RS is transmitted during specific time duration corresponding toa plurality of the scheduled TTIs or timing of a TTI. In this case, allor a part of information on whether a DM-RS or a plurality of DM-RSs tobe transmitted during the time duration are transmitted in a manner ofbeing mapped to the entire REs of a symbol or an RE corresponding to aspecific comb pattern, a DM-RS cyclic shift, an OCC, and comb-patterninformation can be indicated to a UE via higher layer signaling orphysical layer signaling. In this case, specifically, the physical layersignaling may correspond to UL grant DCI that schedules a plurality ofthe UL data channels.

When a plurality of DL data channels for a plurality of TTIs arescheduled by single DL grant DCI, it may be able to define a rule that aDM-RS is to be transmitted at TTIs as many as TTIs determined duringspecific time duration during which a plurality of UL control channelsincluding HARQ-ACK on a plurality of the scheduled DL data channels aretransmitted or a TTI of determined timing only. The number/timing ofTTIs at which a DM-RS is to be transmitted can be defined/promised inadvance by the DL grant DCI or can be indicated by higher layersignaling or the UL grant DCI. In this case, all or a part ofinformation on whether a DM-RS or a plurality of DM-RSs to betransmitted during the time duration are transmitted in a manner ofbeing mapped to the entire REs of a symbol or an RE corresponding to aspecific comb pattern, a DM-RS cyclic shift, an OCC, and comb-patterninformation can be indicated to a UE via higher layer signaling orphysical layer signaling. In this case, specifically, the physical layersignaling may correspond to DL grant DCI that schedules a plurality ofthe DL data channels.

When a plurality of DL data channels for a plurality of TTIs arescheduled by single DL grant DCI, it may be able to define a rule that aDM-RS is to be transmitted in an SC-FDMA symbol only which is determinedwithin specific time duration during which a plurality of UL controlchannels including HARQ-ACK on a plurality of the scheduled DL datachannels are transmitted. An index of the SC-FDMA symbol in which theDM-RS is to be transmitted can be defined/promised in advance or can beindicated by higher layer signaling or the UL grant DCI. For example,the index of the SC-FDMA symbol in which the DM-RS is to be transmittedcan be differently defined/promised according to the number of TTIs atwhich the DM-RS is transmitted within specific time duration duringwhich a plurality of the UL control channels are transmitted or timingof a TTI. In this case, all or a part of information on whether a DM-RSor a plurality of DM-RSs to be transmitted during the time duration aretransmitted in a manner of being mapped to the entire REs of a symbol oran RE corresponding to a specific comb pattern, a DM-RS cyclic shift, anOCC, and comb-pattern information can be indicated to a UE via higherlayer signaling or physical layer signaling. In this case, specifically,the physical layer signaling may correspond to DL grant DCI thatschedules a plurality of the DL data channels.

As mentioned in the foregoing description, if the HARQ-ACK on aplurality of the scheduled DL data channels is transmitted on a singleUL control channel, all or a part of information on an SC-FDMA symbolindex at which a DM-RS is to be positioned for the UL control channel,information on whether a DM-RS is transmitted in a manner of beingmapped to the entire REs of a DM-RS symbol or an RE corresponding to aspecific comb pattern, a DM-RS cyclic shift, an OCC, and a comb patterninformation can be indicated to a UE via higher layer signaling orphysical layer signaling. In this case, specifically, the physical layersignaling may correspond to DL grant DCI that schedules a plurality ofthe DL data channels.

Dynamic DM-RS Insertion

When a short TTI of two symbols is introduced, if a DM-RS occupies onesymbol in every sTTI, it is not preferable in terms of transmissionefficiency. Hence, when a plurality of contiguous sTTIs are scheduled toa UE, a method of dynamically inserting a DM-RS is considering. Inparticular, a network dynamically indicates whether a DM-RS istransmitted in every sTTI via dynamic signaling. It may consider methodsdescribed in the following as a method of indicating the insertion ofthe DM-RS.

As a method, it may be able to define a rule that a specific fieldincluded in UL grant DCI, which schedules a specific sTTI, indicateswhether or not a DM-RS is transmitted for a plurality of sTTIs includingthe specific sTTI. Specifically, this method allows a DM-RS to betransmitted for a plurality of sTTIs among the specific number ofcontiguous sTTIs. Specifically, this method can include a method ofdefining a position of a symbol in which a DM-RS is transmitted byfixing the position in a sTTI in advance.

For example, it may be able to define a DM-RS to be transmitted in amanner of being fixed in a first symbol within an sTTI. If a fieldindicating whether or not a DM-RS is transmitted in each sTTI isconfigured by 4 bits in UL grant DCI, it is able to define a rule that 4bits of the UL grant DCI, which schedules an sTTI #n, can indicatewhether or not a DM-RS is transmitted for 4 contiguous sTTIs includingthe sTTI #n. More generally, it is able to define a rule that the bitmap(i.e., 4 bits in the UL grant DCI) indicates an sTTI at which a DM-RS istransmitted among a plurality of sTTIs which are not contiguous withinspecific time duration (e.g., within 1 subframe or 1 ms).

As a different method, it is able to define a rule that a plurality ofpatterns indicating positions of symbols in which a DM-RS is transmittedare to be defined for a plurality of TTIs corresponding to specific timeduration (e.g., 1 subframe or 1 ms) and one of a plurality of thepatterns is to be indicated. More generally, it is able to define aplurality of patterns of which density and/or a position of a time axisof a DM-RS is different within a plurality of TTIs corresponding tospecific time duration and one of a plurality of the patterns isindicated to select a TTI or a symbol in which a DM-RS is actuallytransmitted within the time duration.

For example, the pattern can be defined as (1) transmitting a DM-RS atall TTIs (in a specific symbol), (2) transmitting a DM-RS in every oddnumbered TTI or every even numbered TTI (in a specific symbol) (in otherword, a DM-RS is transmitted at one TTI in every two TTIs), (3)transmitting a DM-RS at a first TTI within a UL subframe clot (in aspecific symbol), and (4) transmitting a DM-RS at a TTI having a periodof the specific number of TTIs (or the specific number of symbols)defined/configured/signaled by a scheduled TTI in advance. As adifferent example, the pattern can be defined as a DM-RS is to betransmitted (in a specific symbol) at the different number of TTIs amonga plurality of TTIs corresponding to specific time duration. Forexample, a pattern #1 can indicate a DM-RS to be transmitted at TTI #nto TTI#n+3, a pattern #2 can indicate a DM-RS to be transmitted at TTI#n and TTI#n+2, a pattern #3 can indicate a DM-RS to be transmitted atTTI #n+1 and TTI#n+3, and a pattern #4 can indicate a DM-RS to betransmitted at TTI #n.

When a DM-RS transmission is set to a TTI or a specific section, a‘specific symbol’ included in the TTI or the specific section mayindicate all symbols or a first symbol included in the TTI or thespecific section. More specifically, a position to which a DM-RS istransmitted/mapped may vary according to the TTI or the specificsection.

As a further different method, it may not promise/define a position of asymbol in which a DM-RS is transmitted within an sTTI by fixing thesymbol position. In this case, it may be able to define additionalsignaling to indicate a position of a symbol in which a DM-RS istransmitted within an sTTI. For example, when a field indicatinginformation on whether or not a DM-RS is transmitted at each sTTI isconfigured by 3 bits in UL grant DCI, 2 bits of the UL grant DCI forscheduling an sTTI #n indicate one sTTI at which a DM-RS is transmittedand the remaining 1 bit can indicate a symbol to which the DM-RS is tobe mapped among the sTTI at which the DM-RS is transmitted. As adifferent example, 2 bits of the UL grant DCI for scheduling the sTTI #nindicate whether or not a DM-RS is transmitted in each of 2 sTTIsincluding the sTTI #n and the remaining 1 bit can indicate a symbol towhich the DM-RS is to be mapped among the sTTI at which the DM-RS istransmitted. As a further different example, when a field indicatinginformation on whether or not a DM-RS is transmitted at each sTTI isconfigured by 4 bits in UL grant DCI, 2 bits of the UL grant DCI forscheduling an sTTI #n indicate whether or not a DM-RS is transmitted ineach of 2 sTTIs including the sTTI #n and the remaining 2 bits canindicate a symbol to which the DM-RS is to be mapped among symbols ofeach sTTI when the DM-RS is transmitted at each of the two sTTIsincluding the sTTI #n. In case of applying the present method, in orderto more precisely perform channel estimation in a channel situation inwhich time-varying is serious, it may be able to increase a spacebetween symbols to which a DM-RS is mapped to more flexibly transmit aDM-RS.

The physical layer signaling indicating whether or not a DM-RS istransmitted at each of a plurality of TTIs corresponding to specifictime duration (e.g., 1 subframe or 1 ms) may correspond to (1) each ofUL grant DCI that schedules a plurality of the TTIs, (2) UL grant DCIthat schedules one or more predefined/promised TTIs among a plurality ofthe TTIs, or (3) a specific DCI type (slow/first DCI or fast/second DCI)of two-level DCI.

Information on whether or not a DM-RS is transmitted at each of aplurality of TTIs corresponding to specific time duration (e.g., 1subframe or 1 ms) can be indicated by a legacy specific field (e.g., aDM-RS cyclic shift field) included in UL grant DCI or a new field.Specifically, information on whether or not a scheduling target (s) TTIincludes a DM-RS and/or information on a symbol in which a DM-RS istransmitted (in time domain) can be indicated by a specific state of aDM-RS cyclic shift of UL grant DCI.

For example, a plurality of sTTIs belonging to specific time durationcan be configured to use the same DM-RS cyclic shift and/or OCC inadvance. Hence, information on whether or not a DM-RS is transmitted ineach of a plurality of the sTTIs and/or information on a symbol in whicha DM-RS is transmitted can be indicated via the DM-RS cyclic shiftfield.

As a different example, when a short TTI or a dynamic DM-RS insertionoperation is configured, it may be able to configure partial values tobe used only among values of a cyclic shift of a DM-RS and/or an OCC. Apartial bit among 3 bits can indicate information on whether or not aDM-RS is transmitted at each sTTI and/or information on a symbol inwhich a DM-RS is transmitted within an sTTI.

Specifically, information on whether or not a scheduling target (s)TTIincludes a DM-RS and/or information on a symbol in which a DM-RS istransmitted using a frequency hopping flag field (1 bit) included in ULgrant DCI. It may be able to define a rule that the present rule is tobe applied only when a short TTI is configured or a dynamic DM-RSinsertion operation is configured.

Specifically, when sPUSCH scheduling is performed, it may be able todefine a rule that a resource allocation type 1 is not to be used. Inthis case, a resource allocation type field (1 bit) can be configured toindicate information on whether or not a scheduling target (s)TTIincludes a DM-RS and/or information on a symbol in which a DM-RS istransmitted.

As a further different method, it may be able to define a rule that aDM-RS is always to be transmitted without any signaling related toinformation on whether or not a DM-RS is transmitted by default at aspecific sTTI within specific time duration. Specifically, when theDM-RS is always transmitted by default at an sTTI, the sTTI can bedefined by 1 per slot. Or, it may be able to define a rule that a DM-RSis to be transmitted without any signaling by default at a first sTTIonly in each slot. When the remaining sTTIs are scheduled, informationon whether or not the sTTIs include a DM-RS and/or information on asymbol in which a DM-RS is transmitted can be indicated by a DM-RScyclic shift field. In this case, a cyclic shift and/or an OCC used fortransmitting a DM-RS (1) can be defined to be identical to that of aDM-RS which is transmitted by default within specific time duration, (2)can be defined to be identical to that of a DM-RS which is transmittedby default immediately before the DM-RS, (3) can be defined bypredefined values, or (4) can be defined by values induced using anidentifier (e.g., RNTI) of a UE.

Detail Explanation on Dynamic DM-RS Insertion

When a plurality of sTTIs are scheduled to a UE, a dynamic DM-RSinsertion method can be introduced to make a network indicateinformation on whether or not a DM-RS is transmitted in every sTTI usingdynamic signaling. The signaling method is explained in more detail inthe following.

As a method, it may be able to define a rule that a specific fieldincluded in UL grant DCI, which schedules a specific sTTI, indicateswhether or not a DM-RS is transmitted for each of a plurality of sTTIsincluding the specific sTTI. For example, it may be able to define arule that a specific field included in UL grant DCI, which schedules ansTTI #n, indicates whether or not a DM-RS is transmitted for a pluralityof sTTIs including “the sTTI #n, sTTI(s) appearing before the sTTI #n,and/or sTTI(s) appearing after the sTTI #n” such as {sTTI #n−2, sTTI#n−1, sTTI #n, sTTI #n+1}, {sTTI #n−1, sTTI #n, sTTI #n+1, sTTI #n+2},or {sTTI #n, sTTI #n+1, sTTI #n+2, sTTI #n+3}. In this case, a DM-RStransmission method (PRB allocation and/or power allocation and/orcyclic shift and/or OCC, etc.) may follow a configuration at a scheduletarget sTTI of UL grant DCI, follow a configuration indicated by ULgrant DCI, or can be configured by higher layer signaling in advance.For example, a DM-RS transmission TTI indicated by the UL grant DCI canbe indicated in a form of a relative time offset from a schedulingtarget TTI. More specifically, the time offset may correspond to a unitof sTTI.

As mentioned in the foregoing description, according to an operation ofdynamic DM-RS insertion, since a specific sTTI does not include a DM-RS,it may be necessary for an eNB to borrow a channel estimation result ina DM-RS from a different sTTI in which DM-RS transmission is included.More generally, when a plurality of sTTIs perform channel estimation ora different operation by sharing a DM-RS symbol, the channel estimationor the different operation can be supported only when DM-RS-relatedconfiguration information on a plurality of the sTTIs and resourceallocation satisfy a prescribed condition. In order to support theoperation, it is necessary for a UE and an eNB to identically understandan operation described in the following.

When a plurality of sTTIs are scheduled to a UE during specific timeduration to support dynamic DM-RS insertion, the UE may assume that astate of a DM-RS cyclic shift is to be identically set to a plurality ofthe sTTIs. And, when a plurality of sTTIs are scheduled to a UE duringspecific time duration, the UE may assume that resource allocation is tobe identically indicated to a plurality of the sTTIs. Or, when resourceallocation is performed on a plurality of the sTTIs, the UE may assumethat resource allocation of an sTTI not including a DM-RS is to be asubset of resource allocation of an sTTI including a DM-RS.

Detail Explanation on Dynamic DM-RS Insertion

As a method, a specific field included in UL grant DCI, which schedulesa specific sTTI, can indicate a symbol in which a DM-RS istransmittable. And, a candidate symbol in which a DM-RS is transmittablecan be restricted to a specific symbol included in a scheduled sTTI, aspecific symbol included in an sTTI immediately before the scheduledsTTI, and a specific symbol included in an sTTI immediately after thescheduled sTTI on the basis of the scheduled sTTI.

As a scheme of configuring a state of a specific included in the ULgrant DCI, it may consider (1) first symbol of the scheduled sTTI, (2)last symbol of the scheduled sTTI, (3) last symbol of the sTTIimmediately before the scheduled sTTI, (4) first symbol of the sTTIimmediately after the scheduled sTTI, (5) (predefined/promised) specificsymbol of the scheduled sTTI except the first symbol and the lastsymbol, and (6) a state of not transmitting a DM-RS. As described in (1)and (2), the first and the last symbol are considered as a DM-RStransmission candidate symbol. This is because, when decoding isperformed, it is necessary to easily share a DM-RS with the sTTIimmediately before the scheduled sTTI or the sTTI immediately after thescheduled sTTI.

Fallback/Default UE Operation

When a UE misses UL grant DCI for a specific sTTI, if the specific sTTIincludes DM-RS transmission and the remaining sTTIs do not include DM-RStransmission, since DM-RS for the remaining sTTIs does not exist, an eNBmay fail to perform UL demodulation. Hence, it is necessary to define anoperation in consideration of the abovementioned situation.

As a proposal, in order to make a UE recognize a situation that aplurality of sTTIs are scheduled to a UE during specific time duration,it may be able to define a rule that such a signal as a UL assignmentindicator is to be indicated via UL grant DCI. Specifically, when aplurality of contiguous sTTIs are scheduled or a plurality of sTTIs arescheduled within predefined/signaled time duration, the UL assignmentindicator can indicate whether or not a plurality of the sTTIs arescheduled in an ascending order or a descending order.

When a specific sTTI is scheduled to a UE, if the UE recognizes that theUE has missed scheduling DCI for a previous sTTI via the UL assignmentindicator, it is able to define a rule that the UE transmits a DM-RS toa predefined/signaled time/frequency resource at the specific sTTI.Although the UE is indicated not to transmit a DM-RS at the specificsTTI, the UE can transmit the DM-RS at the specific sTTI by ignoring theindication. In this case, it may be able to define a rule that the DM-RSis to be transmitted in a manner of puncturing (or rate matching) datain a predefined/signaled time/frequency resource. More specifically, incase of performing rate matching on data, it may be able to map the datato a time/frequency resource rather than a time/frequency resource whichis signaled via predefined/promised higher layer signaling/physicallayer signaling irrespective of whether or not a DM-RS is transmitted.In this case, it may obtain a gain in terms of transmit power of the UE.Data mapping can be differently configured via higher layer/physicallayer signaling.

As a further different method, when a specific sTTI is scheduled to aUE, if the UE does not receive any scheduling for more than prescribedtime, the UE can transmit a DM-RS at the scheduled sTTI (i.e.,scheduling target sTTI) irrespective of whether or not a DM-RS indicatedby UL grant DCI is transmitted. In this case, it may be able to define arule that the DM-RS is to be transmitted in a manner of puncturing (orrate matching) data. More specifically, in case of performing ratematching on data, it may be able to map the data to a time/frequencydata rather than a time/frequency resource which is signaled viapredefined/promised higher layer signaling/physical layer signalingirrespective of whether or not a DM-RS is transmitted. In this case, itmay obtain a gain in terms of transmit power of the UE. Data mapping canbe differently configured via higher layer/physical layer signaling.

Definition of separate sequences per resource with cyclic shift hopping

Separate Sequences Generation Per Resource with Cyclic Shift Hopping

When a plurality of TTIs transmit a DM-RS in the same symbol, a basesequence for generating a DM-RS sequence for a TTI can be determined notby a total size of resources allocated for a UL channel (e.g., PUSCH)but by a resource unit (e.g., X PRB) having a predefined/promisedspecific size. In particular, the base sequence, which is determined bythe resource unit having the predefined/promised specific size, can bemapped/transmitted in a manner of being repeated as much as the size inallocated UL resources.

In this case, PAPR can be increase in a symbol in which a DM-RS istransmitted. In order to minimize the increase of the PAPR, it may beable to define a rule that a different (independent) cyclic shift is tobe applied to the same DM-RS sequence which is determined according to aresource unit having a specific size. Referring to FIG. 17, a PRB index{0,1,2,3} and a PRB index {2,3,4,5} are respectively assigned to a TTI#n and a TTI #n+1 as a PUSCH resource. DM-RS sequences for two TTIs aretransmitted to the same symbol in a manner of being multiplexed using adifferent cyclic shift while the same base sequence is used in a unit of2 PRBs.

Although the examples for the proposed schemes correspond toexplanation/description on PUSCH and/or PUSCH DM-RS, the examples canalso be applied to PUCCH and/or PUCCH DM-RS. And, although a part of theproposed schemes has been explained with a method that two adjacent TTIstransmit a DM-RS in the same symbol, the method can also be applied to amethod that three or more TTIs transmit a DM-RS in the same symbol.

Since it is able to include the examples for the proposed method as oneof implementation methods of the present invention, it is apparent thatthe examples are considered as a sort of proposed methods. Although theembodiments of the present invention can be independently implemented,the embodiments can also be implemented in a combined/aggregated form ofa part of embodiments. It may define a rule that an eNB/location serverinforms a UE of information on whether to apply the proposed methods(or, information on rules of the proposed methods) via a predefinedsignal (e.g., physical layer signal or higher layer signal).

FIG. 18 is a flowchart illustrating an operation of a terminal.

The terminal may receive configuration information on an uplinkreference signal for a plurality of TTIs from a base station [S1810].The terminal may transmit an uplink reference signal in at least one TTIamong the plurality of TTIs using the received configuration information[S1820]. The configuration information may be included in signaling thatschedules at least one TTI among the plurality of TTIs.

The uplink reference signal may be transmitted in each of symbols of theat least one TTI.

The configuration information may be included in downlink controlinformation that schedules a TTI from among the plurality of TTIs. Or,the configuration information includes a bit field that indicates TTIsin which the uplink reference signal is to be transmitted. The bit fieldmay indicate whether or not the uplink reference signal is transmittedin each of a predetermined number of contiguous TTIs including a TTIscheduled by the configuration information.

The configuration information indicates one of a plurality of candidatepatterns in which the uplink reference signal is to be transmitted andeach of a plurality of the candidate patterns may indicate a TTI ofprescribed time duration during which the uplink reference signal istransmitted or a symbol in the TTI.

The method may further include the step of receiving information on asymbol in at least one TTI at which the uplink reference signal is to betransmitted.

The configuration information includes a bit field indicating a symbolin a TTI at which the uplink reference signal is to be transmitted andthe bit field may indicate symbols of the predetermined number ofcontiguous TTIs including the TTI scheduled by the configurationinformation.

And, configuration information to be used for transmitting the uplinkreference signal may be included in signaling that schedules apredetermined TTI from among a plurality of the TTIs.

The configuration information may be included in signaling thatschedules a TTI to which a largest uplink transmission resource isallocated from among the plurality of TTIs.

The terminal may expect that signaling scheduling the plurality of TTIsindicate configuration information on the same uplink reference signal.

The configuration information may include at least one selected from thegroup consisting of a cyclic shift, an OCC (orthogonal cover code),transmit power, RE (resource element) mapping of uplink referencesignal, and resource allocation.

FIG. 19 is a block diagram illustrating a transmitting device 10 and areceiving device 20 configured to implement embodiments of the presentinvention. Each of the transmitting device 10 and receiving device 20includes a transmitter/receiver 13, 23 capable of transmitting orreceiving a radio signal that carries information and/or data, a signal,a message, etc., a memory 12, 22 configured to store various kinds ofinformation related to communication with a wireless communicationsystem, and a processor 11, 21 operatively connected to elements such asthe transmitter/receiver 13, 23 and the memory 12, 22 to control thememory 12, 22 and/or the transmitter/receiver 13, 23 to allow the deviceto implement at least one of the embodiments of the present inventiondescribed above.

The memory 12, 22 may store a program for processing and controlling theprocessor 11, 21, and temporarily store input/output information. Thememory 12, 22 may also be utilized as a buffer. The processor 11, 21controls overall operations of various modules in the transmittingdevice or the receiving device. Particularly, the processor 11, 21 mayperform various control functions for implementation of the presentinvention. The processors 11 and 21 may be referred to as controllers,microcontrollers, microprocessors, microcomputers, or the like. Theprocessors 11 and 21 may be achieved by hardware, firmware, software, ora combination thereof. In a hardware configuration for an embodiment ofthe present invention, the processor 11, 21 may be provided withapplication specific integrated circuits (ASICs) or digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), and field programmable gate arrays(FPGAs) that are configured to implement the present invention. In thecase which the present invention is implemented using firmware orsoftware, the firmware or software may be provided with a module, aprocedure, a function, or the like which performs the functions oroperations of the present invention. The firmware or software configuredto implement the present invention may be provided in the processor 11,21 or stored in the memory 12, 22 to be driven by the processor 11, 21.

The processor 11 of the transmitter 10 performs predetermined coding andmodulation of a signal and/or data scheduled by the processor 11 or ascheduler connected to the processor 11, and then transmits a signaland/or data to the transmitter/receiver 13. For example, the processor11 converts a data sequence to be transmitted into K layers throughdemultiplexing and channel coding, scrambling, and modulation. The codeddata sequence is referred to as a codeword, and is equivalent to atransport block which is a data block provided by the MAC layer. Onetransport block is coded as one codeword, and each codeword istransmitted to the receiving device in the form of one or more layers.To perform frequency-up transformation, the transmitter/receiver 13 mayinclude an oscillator. The transmitter/receiver 13 may include Nttransmit antennas (wherein Nt is a positive integer greater than orequal to 1).

The signal processing procedure in the receiving device 20 is configuredas a reverse procedure of the signal processing procedure in thetransmitting device 10. The transmitter/receiver 23 of the receivingdevice 20 receives a radio signal transmitted from the transmittingdevice 10 under control of the processor 21. The transmitter/receiver 23may include Nr receive antennas, and retrieves baseband signals byfrequency down-converting the signals received through the receiveantennas. The transmitter/receiver 23 may include an oscillator toperform frequency down-converting. The processor 21 may perform decodingand demodulation on the radio signal received through the receiveantennas, thereby retrieving data that the transmitting device 10 hasoriginally intended to transmit.

The transmitter/receiver 13, 23 includes one or more antennas. Accordingto an embodiment of the present invention, the antennas function totransmit signals processed by the transmitter/receiver 13, 23 are toreceive radio signals and deliver the same to the transmitter/receiver13, 23. The antennas are also called antenna ports. Each antenna maycorrespond to one physical antenna or be configured by a combination oftwo or more physical antenna elements. A signal transmitted through eachantenna cannot be decomposed by the receiving device 20 anymore. Areference signal (RS) transmitted in accordance with a correspondingantenna defines an antenna from the perspective of the receiving device20, enables the receiving device 20 to perform channel estimation on theantenna irrespective of whether the channel is a single radio channelfrom one physical antenna or a composite channel from a plurality ofphysical antenna elements including the antenna. That is, an antenna isdefined such that a channel for delivering a symbol on the antenna isderived from a channel for delivering another symbol on the sameantenna. An transmitter/receiver supporting the Multiple-InputMultiple-Output (MIMO) for transmitting and receiving data using aplurality of antennas may be connected to two or more antennas.

In embodiments of the present invention, the UE or the terminal operatesas the transmitting device 10 on uplink, and operates as the receivingdevice 20 on downlink. In embodiments of the present invention, the eNBor the base station operates as the receiving device 20 on uplink, andoperates as the transmitting device 10 on downlink.

The transmitting device and/or receiving device may be implemented byone or more embodiments of the present invention among the embodimentsdescribed above.

Detailed descriptions of preferred embodiments of the present inventionhave been given to allow those skilled in the art to implement andpractice the present invention. Although descriptions have been given ofthe preferred embodiments of the present invention, it will be apparentto those skilled in the art that various modifications and variationscan be made in the present invention defined in the appended claims.Thus, the present invention is not intended to be limited to theembodiments described herein, but is intended to have the widest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to wireless communication devicessuch as a terminal, a relay, and a base station.

1. A method of transmitting an uplink reference signal for a terminalconfigured to support multiple TTI (transmission time interval) lengthsin a wireless communication system, comprising: receiving configurationinformation on an uplink reference signal for a plurality of TTIs from abase station; and transmitting an uplink reference signal in at leastone TTI from among the plurality of TTIs using the receivedconfiguration information, wherein the configuration information isincluded in signaling that schedules the at least one TTIs from amongthe plurality of TTIs, wherein the configuration information includes abit field indicating TTIs in which the uplink reference signal is to betransmitted, and wherein the bit field indicates whether or not theuplink reference signal is transmitted in each of a predetermined numberof contiguous TTIs including a TTI scheduled by the configurationinformation.
 2. The method of claim 1, wherein the uplink referencesignal is transmitted in a symbol of each of the at least one TTI. 3.The method of claim 1, wherein the configuration information is includedin downlink control information that schedules a TTI from among theplurality of TTIs.
 4. (canceled)
 5. The method of claim 1, wherein theconfiguration information indicates one of a plurality of candidatepatterns in which the uplink reference signal is to be transmitted, andwherein each of the plurality of candidate patterns indicates a TTI or asymbol of a TTI, included in a predetermined time duration in which theuplink reference signal is transmitted.
 6. The method of claim 1,further comprising receiving information on a symbol of the at least oneTTI in which the uplink reference signal is to be transmitted.
 7. Themethod of claim 1, wherein the configuration information includes a bitfield indicating a symbol of a TTI in which the uplink reference signalis to be transmitted, and wherein the bit field indicates symbols of apredetermined number of contiguous TTIs including a TTI scheduled by theconfiguration information.
 8. The method of claim 1, whereinconfiguration information to be used for transmitting the uplinkreference signal is included in signaling that schedules a predeterminedTTI from among the plurality of TTIs.
 9. The method of claim 1, whereinthe configuration information is contained in signaling that schedules aTTI to which a largest uplink transmission resource is allocated, fromamong the plurality of TTIs.
 10. The method of claim 1, wherein theterminal expects that signaling for scheduling the plurality of TTIsindicates configuration information on the same uplink reference signal.11. The method of claim 1, wherein the configuration informationincludes at least one selected from the group consisting of a cyclicshift, an OCC (orthogonal cover code), transmit power, RE (resourceelement) mapping of an uplink reference signal, and resource allocation.12. A terminal configured to support multiple TTI (transmission timeinterval) lengths in a wireless communication system, comprising: atransmitter and a receiver; and a processor that controls thetransmitter and the receiver, the processor controls the receiver toreceive configuration information on an uplink reference signal for aplurality of TTIs from a base station, controls the transmitter totransmit an uplink reference signal in at least one TTI from among theplurality of TTIs using the received configuration information, whereinthe configuration information is contained in signaling that schedulesthe at least one TTIs from among the plurality of TTIs, wherein theconfiguration information includes a bit field indicating TTIs in whichthe uplink reference signal is to be transmitted, and wherein the bitfield indicates whether or not the uplink reference signal istransmitted in each of a predetermined number of contiguous TTIsincluding a TTI scheduled by the configuration information.